Magnetic memory

ABSTRACT

According to one embodiment, a device includes a member including a first portion having a first dimension in first direction, a second portion spaced from the first portion and having a second dimension in the first direction, a third portion between the first and second portions and having a third dimension in the first direction, and a fourth portion between the first and third portions and having a fourth dimension in the first direction; and a circuit to supply a shift pulse including first and second pulses to the member and move a domain wall in the member. The third dimension is less than the first dimension. The second and fourth dimensions are less than the third dimension. A second value of the second pulse is less than a first value of the first pulse.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2020-050852, filed Mar. 23, 2020, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetic memory.

BACKGROUND

Research and development of a magnetic memory using a magnetic memberhas been promoted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a configuration example of a magneticmemory of a first embodiment.

FIG. 2 is an equivalent circuit diagram of a memory cell array of themagnetic memory of the first embodiment.

FIG. 3 is a bird's-eye view illustrating a configuration example of amemory cell unit of the magnetic memory of the first embodiment.

FIG. 4 is a cross-sectional view illustrating a configuration example ofthe memory cell unit of the magnetic memory of the first embodiment.

FIG. 5 is a cross-sectional process view illustrating a fabrication stepof a manufacturing method of the magnetic memory of the firstembodiment.

FIG. 6 is a view for explaining the manufacturing method of the magneticmemory of the first embodiment.

FIG. 7, FIG. 8 and FIG. 9 are cross-sectional process views illustratingfabrication steps of the manufacturing method of the magnetic memory ofthe first embodiment.

FIG. 10 is a view for explaining an operation example of the magneticmemory of the first embodiment.

FIG. 11 and FIG. 12 are views illustrating pulse waveforms used in theoperation of the magnetic memory of the first embodiment.

FIG. 13, FIG. 14, FIG. 15, FIG. 16, FIG. 17, FIG. 18 and FIG. 19 areviews for explaining an operation example of the magnetic memory of thefirst embodiment.

FIG. 20 is a view illustrating an example of a magnetic memory of asecond embodiment.

FIG. 21 is cross-sectional view illustrating a configuration example ofa magnetic memory of a third embodiment.

FIG. 22, FIG. 23 and FIG. 24 are cross-sectional process viewsillustrating fabrication steps of a manufacturing method of the magneticmemory of the third embodiment.

FIG. 25 is a cross-sectional view illustrating a configuration exampleof a magnetic memory of a fourth embodiment.

FIG. 26 is a schematic view illustrating a configuration example of amagnetic memory of a fifth embodiment.

FIG. 27, FIG. 28 and FIG. 29 are views illustrating modifications of themagnetic memories of the embodiments.

DETAILED DESCRIPTION

Referring to FIG. 1 to FIG. 29, magnetic memories of embodiments will bedescribed.

In the description below, elements having the same function andstructure are denoted by the same reference sign.

In addition, in each embodiment below, when constituent elements (e.g.circuits, interconnects, and various voltages and signals), which aredenoted by reference signs ending with numerals/alphabetical charactersfor distinction, do not need to be distinguished, expressions (referencesigns) without such numerals/alphabetical characters at the ends areused.

In general, according to one embodiment, a magnetic device includes amagnetic member including a first portion with a first dimension in afirst direction, a second portion spaced from with the first portion ina second direction crossing the first direction and having a seconddimension in the first direction, a third portion provided between thefirst portion and the second portion and having a third dimension in thefirst direction, and a fourth portion provided between the first portionand the third portion and having a fourth dimension in the firstdirection; and a circuit configured to supply a shift pulse including afirst pulse and a second pulse to the magnetic member, and to move adomain wall in the magnetic member in the second direction, wherein thethird dimension is less than the first dimension, and the seconddimension and the fourth dimension is less than the third dimension, andthe first pulse has a first current value, and the second pulse has asecond current value which is less than the first current value.

Embodiments (1) First Embodiment

Referring to FIG. 1 to FIG. 19, a magnetic memory of a first embodimentand a control method thereof will be described.

(a) Configuration Example

Referring to FIG. 1 to FIG. 4, a configuration example of the magneticmemory of the present embodiment will be described.

(a-1) Entire Configuration

FIG. 1 is a block diagram illustrating a configuration example of themagnetic memory of the present embodiment.

For example, a magnetic memory 1 of the present embodiment is a domainwall memory.

As illustrated in FIG. 1, the domain wall memory (also referred to as“domain wall shift memory”) 1 of the embodiment includes a memory cellarray (also referred to as “memory area”) 100, a row control circuit110, a column control circuit 120, a write circuit 140, a read circuit150, a shift circuit 160, an I/O circuit 170, a voltage generator 180,and a control circuit 190.

The memory cell array 100 includes a plurality of magnetic members 50and a plurality of interconnects. Each magnetic member 50 is connectedto a corresponding one or more interconnects (e.g. a word line and a bitline). Data is stored in a memory cell MC in the magnetic member 50.

The row control circuit 110 controls rows of the memory cell array 100.A decoded result (row address) of an address is supplied to the rowcontrol circuit 110. The row control circuit 110 sets a row (e.g. a wordline), which is based on the decoded result of the address, in aselected state. Hereinafter, the row (or word line) set in the selectedstate is referred to as “selected row” (or “selected word line”). A rowother than the selected row is referred to as “non-selected row” (or“non-selected word line”).

For example, the row control circuit 110 includes a multiplexer (a wordline selection circuit) and a word line driver.

The column control circuit 120 controls columns of the memory cell array100. A decoded result (column address) of an address from the controlcircuit 190 is supplied to the column control circuit 120. The columncontrol circuit 120 sets a column (e.g. at least one bit line), which isbased on the decoded result of the address, in a selected state.Hereinafter, the column (or bit line) set in the selected state isreferred to as “selected column” (or “selected bit line”). A columnother than the selected column is referred to as “non-selected column”(or “non-selected bit line”).

The column control circuit 120 includes a multiplexer (a bit lineselection circuit) and a bit line driver.

The write circuit (also referred to as “write control circuit” or “writedriver”) 140 executes various controls for a write operation (write ofdata). At a time of a write operation, the write circuit 140 supplies awrite pulse, which is formed by current and/or voltage, to the memorycell array 100. Thereby, data is written in the memory cell array 100(in memory cells).

For example, the write circuit 140 is connected to the memory cell array100 via the row control circuit 110.

The write circuit 140 includes a voltage source and/or current source, apulse generator, a latch circuit, and the like.

The read circuit (also referred to as “read control circuit” or “readdriver”) 150 executes various controls for a read operation (read ofdata). At a time of a read operation, the read circuit 150 supplies aread pulse (e.g. read current) to the memory cell array 100. The readcircuit 150 senses a potential or a current value of a bit line BL.Based on the sensed result, data in the magnetic member 50 is read.

For example, the read circuit 150 is connected to the memory cell array100 via the column control circuit 120.

The read circuit 150 includes a voltage source and/or current source, apulse generator, a latch circuit, a sense amplifier circuit, and thelike.

The shift circuit (also referred to as “shift control circuit” or “shiftdriver”) 160 executes various controls for a shift operation (shift ofdata). At a time of shift operation, the shift circuit 160 supplies tothe memory cell array 100 a pulse (hereinafter referred to as “shiftpulse”) for moving a domain wall (magnetic domain) in the magneticmember 50.

For example, the shift circuit 160 is connected to the memory cell array100 via the row control circuit 110 and the column control circuit 120.

The shift circuit 160 includes a voltage source and/or current source, apulse generator, and the like.

Note that the write circuit 140, read circuit 150 and shift circuit 160are not limited to mutually independent circuits. For example, the writecircuit, read circuit and shift circuit may include common structuralelements which are mutually usable, and may be disposed in the domainwall memory 1 as a single integral circuit.

The I/O circuit (input/output circuit) 170 is an interface circuit fortransferring various signals.

At a time of a write operation, the I/O circuit 170 transfers, as writedata, data DT from an external device (a controller or a host device) 2to the write circuit 140. At a time of a read operation, the I/O circuit170 transfers data, which is output from the memory cell array 100 tothe read circuit 150, to the external device 2 as read data. The I/Ocircuit 170 transfers an address ADR and a command CMD from the externaldevice 2 to the control circuit 190. The I/O circuit 170 transfersvarious control signals CNT between the control circuit 190 and theexternal device 2.

The voltage generator 180 generates voltages for various operations ofthe memory cell array 100, by using a power supply voltage which isprovided from the external device 2 (or power supply). For example, at atime of a write operation, the voltage generator 180 outputs variousvoltages, which are generated for the write operation, to the writecircuit 140. At a time of a read operation, the voltage generator 180outputs various voltages, which are generated for the read operation, tothe read circuit 150. At a time of a shift operation, the voltagegenerator 180 outputs various voltages, which are generated for theshift operation, to the shift circuit 160.

The control circuit (also referred to as “state machine”, “sequencer” or“internal controller”) 190 controls operations of respective circuits inthe memory device 1, based on the control signal CNT, address ADR andcommand CMD.

The control circuit 190 includes, for example, a command decoder, anaddress decoder, and a latch circuit.

For example, the command CMD is a signal indicative of an operationwhich the domain wall memory 1 is to execute. For example, the addressADR is a signal indicative of coordinates of at least one memory cell(hereinafter referred to as “selected cell”) which is an operationtarget in the memory cell array 100. The address ADR includes a rowaddress and a column address of a selected cell. For example, thecontrol signal CNT is a signal for controlling an operation timingbetween the magnetic memory 1 and the external device 2, and anoperation timing in the inside of the magnetic memory 1.

(a-2) Memory Cell Array

Referring to FIG. 2 to FIG. 4, a description will be given of aconfiguration example of the memory cell array of the domain wall memoryof the present embodiment.

FIG. 2 is a schematic view illustrating a configuration example of thememory cell array in the domain wall memory of the present embodiment.

As illustrated in FIG. 2, in the domain wall memory of the embodiment,magnetic members 50 are provided in the memory cell array 100.

The magnetic members 50 are arranged two-dimensionally in the memorycell array 100 on a substrate (not shown). Each magnetic member 50extends in a direction (Z direction) perpendicular to an upper surface(X-Y plane) of the substrate.

Word lines WL and bit lines BL are provided in the memory cell array100. The word lines WL are arranged in a Y direction. The word lines WLextend in an X direction. The bit lines BL are arranged in the Xdirection. The bit lines BL extend in the Y direction. The bit lines BLare provided above the word lines WL in the Z direction.

The magnetic members 50 are provided between the word lines WL and bitlines BL. One end of each magnetic member 50 is connected to thecorresponding word line WL. The other end of the magnetic member 50 isconnected to the corresponding bit line BL. The magnetic members 50arranged in the X direction are connected to the same word line WL. Themagnetic members 50 arrange in the Y direction are connected to the samebit line BL.

For example, a reproducing element 10 and a switching element 20 areconnected between the bit line BL and the magnetic member 50.

The reproducing element 10 is provided between the magnetic member 50and the switching element 20. The reproducing element 10 is electricallyconnected to the magnetic member 50 and the switching element 20. Forexample, the reproducing element 10 is connected to the magnetic member50 via a magnetic layer 59.

At a time of a read operation of the domain wall memory 1, thereproducing element 10 functions as an element (hereinafter, alsoreferred to as “read element”) for reading data in the magnetic member50.

The switching element 20 is provided between the reproducing element 10and the bit line BL. The switching element 20 is electrically connectedto the reproducing element 10 and the bit line BL.

The switching element 20 is used to control a connection between themagnetic member 50 and the bit line BL. When the switching element 20 isset in the ON state, the magnetic member 50 is electrically connected tothe bit line BL. When the switching element 20 is set in the OFF state,the magnetic member 50 is electrically disconnected from the bit lineBL.

For example, the ON/OFF of the switching element 20 is controlled by thecontrol of a potential difference between the bit line BL and the wordline WL. Thereby, one or more magnetic members, which are operationtargets among the magnetic members 50 of the memory cell array 100, areselected (activated).

A conductive layer (interconnect) FL is provided above the magneticlayer 59 in the Z direction. The conductive layer FL extends in the Xdirection, for example, in a region between the bit line BL and themagnetic layer 59. The conductive layer FL extends over a plurality ofmagnetic layers 59.

The conductive layer FL is an interconnect for data write (hereinafter,also referred to as “write line” or “field line”) by a magnetic fieldwrite method at a time of a write operation of the domain wall memory 1.At the time of the write operation by the magnetic field write method, awrite pulse (hereinafter, also referred to as “write current”) issupplied to the write line FL. By the write current, a magnetic field isgenerated around the write line FL. The generated magnetic field isapplied to the magnetic layer 59. In accordance with the direction ofthe generated magnetic field, the direction of magnetization MM of themagnetic layer 59 and the magnetic member 50, which is connected to themagnetic layer 59, is set. Thereby, data is written in the magneticmember 50.

The direction of the magnetic field changes in accordance with thedirection of a write current in the write line FL. Therefore, thedirection, in which the write current flows in the write line FL, is setin accordance with the data to be written.

A plurality of memory cells MC are provided in each magnetic member 50.The memory cells MC are arranged in the Z direction in the magneticmember 50. Thereby, the memory cells MC are arranged three-dimensionallyin the memory cell array 100.

Each of the memory cells MC includes a cell region (also referred to as“cell portion” or “data retention portion”) 510. The cell region 510 isa region (portion) provided in the magnetic member 50 in a manner tocorrespond to the memory cell MC. The cell region 510 is a magneticregion (magnetic portion) capable of having magnetization MM.

When the memory cell MC stores data, the cell region 510 hasmagnetization MM. The data stored in the memory cell MC is associatedwith the direction of magnetization MM of the cell region 510.

The magnetic member 50 has perpendicular magnetic anisotropy or in-planemagnetic anisotropy. The magnetization easy axis direction of the cellregion 510 corresponds to the magnetic anisotropy of the magnetic member50.

Hereinafter, a structure including at least one or more memory cells MCprovided in the magnetic member 50, the reproducing element 10 and theswitching element 20 is referred to as “memory cell unit” (or “memorycell string”) MU.

(a-3) Memory Cell Unit

FIG. 3 is a schematic bird's-eye view illustrating a configurationexample of the memory cell unit in the domain wall memory of the presentembodiment. FIG. 4 is a schematic cross-sectional view illustrating aconfiguration example of the memory cell unit in the domain wall memoryof the embodiment.

As illustrated in FIG. 3 and FIG. 4, the magnetic member 50 is providedabove a substrate 9 in the Z direction. The magnetic member 50 includesa magnetic layer (hereinafter, also referred to as “domain wall motionlayer) 500. The magnetic member 50 extends in the Z direction. Forexample, the magnetic member 50 has a cylindrical structure. A centeraxis of the cylindrical magnetic member 50 extends in the Z direction.However, the center axis of the magnetic member 50 may incline withrespect to the Z direction.

For example, the magnetic member 50 is interposed between two insulators93 and 95 in a direction parallel to the upper surface of the substrate9.

Note that the insulator 93 may not be provided. In this case, a cavityis provided in the magnetic member 50.

For example, the material of the magnetic member 50 is a materialincluding at least one element selected from the group consisting ofcobalt (Co), iron (Fe), nickel (Ni), manganese (Mn) and chromium (Cr),and at least one element selected from the group consisting of platinum(Pt), palladium (Pd), iridium (Ir), ruthenium (Ru) and rhodium (Rh). Amore concrete example of the material of the magnetic member 50 is CoPt,CoCrPt, FePt, CoPd, or FePd. Note that the material of the magneticmember 50 is not limited to the above-described materials, and may beother magnetic materials.

For example, the magnetic layer constituting the magnetic member 50 maybe a stacked film. For example, the magnetic member 50 includes amagnetic film and a nonmagnetic film. The magnetic film is providedbetween the nonmagnetic film (e.g. a hafnium oxide film) and theinsulator 95. However, the magnetic film may be provided between thenonmagnetic film and the insulator 93. The magnetic member 50 may be amagnetic film of a single layer.

For example, when the magnetic member 50 has perpendicular magneticanisotropy, the magnetization of the magnetic member 50 is directed in adirection from the center of the magnetic member 50 toward an outerperiphery of the magnetic member 50, or in a direction from the outerperiphery of the magnetic member 50 toward the center of the magneticmember 50.

The cell region 510 corresponding to each memory cell MC is provided inthe magnetic member 50. The magnetic member 50 includes memory cells MC.One memory cell MC is provided in one cell region 510.

The magnetic layer 59 is provided on the magnetic member 50 in the Zdirection. For example, the magnetic layer 59 has a circular plan-viewshape, as viewed in the Z direction. However, the magnetic layer 59 mayhave a rectangular plan-view shape. For example, a dimension of themagnetic layer 59 in a direction parallel to the surface of thesubstrate 9 is greater than a dimension D1 of the magnetic member 50 inthe direction parallel to the surface of the substrate 9.

The magnetic layer 59 is connected to the magnetic member 50. Forexample, the magnetic layer 59 is a layer which is continuous with themagnetic member 50.

The magnetization of the magnetic layer 59 changes in accordance withthe magnetization of the magnetic member 50. For example, as regards themagnetization easy axis direction of each layer, the direction ofmagnetization of the magnetic layer 59 is identical to the direction ofmagnetization of a cell region 510A which is directly connected to themagnetic layer 59. The cell region 510A directly connected to themagnetic layer 59 corresponds to a memory cell MCA which is locatedclosest to the bit line side among the memory cells in the memory cellunit MU.

In the example of FIG. 3, the memory cell MCA functions as a read cellat a time of a read operation, and functions as a write cell at a timeof a write operation. The read cell is a memory cell for temporarilystoring data from a memory cell of a read target at a time of a readoperation. The write cell is a memory cell in which write data istemporarily written at a time of a write operation.

A stacked body including the reproducing element 10 and switchingelement 20 is provided on the magnetic layer 59.

The reproducing element 10 is a magnetoresistive effect element.

The magnetoresistive effect element 10 is provided on the magnetic layer59 in the Z direction. For example, the magnetoresistive effect element10 is disposed in such a position as not to overlap the magnetic member50 in the Z direction. The magnetoresistive effect element 10 may bedisposed in such a position as to overlap the magnetic member 50 in theZ direction. The magnetoresistive effect element 10 is disposed on oneend side in the Y direction of the magnetic layer 59.

The magnetoresistive effect element 10 is electrically connected to themagnetic layer 59.

For example, the magnetoresistive effect element 10 includes twomagnetic layers 11 and 12 and a nonmagnetic layer 13. The nonmagneticlayer 13 is provided between the two magnetic layers 11 and 12 in the Zdirection. The two magnetic layers 11 and 12 and nonmagnetic layer 13form a magnetic tunnel junction (MTJ). Hereinafter, the magnetoresistiveeffect element 10 including the magnetic tunnel junction is referred toas “MTJ element”. The nonmagnetic layer 13 of the MTJ element 10 isreferred to as “tunnel barrier layer”.

The magnetic layers 11 and 12 are, for example, ferromagnetic layersincluding cobalt, iron and boron. The magnetic layer 11, 12 may be asingle-layer film, or a multilayer film (e.g. artificial lattice film).The tunnel barrier layer 13 is, for example, an insulating filmincluding magnesium oxide. The tunnel barrier layer 13 may be asingle-layer film or a multilayer film.

Each magnetic layer 11, 12 has in-plane magnetic anisotropy orperpendicular magnetic anisotropy.

For example, when the magnetic layer 11, 12 has in-plane magneticanisotropy, the magnetization easy axis direction of the magnetic layer11, 12 having in-plane magnetic anisotropy is substantially parallel toa layer surface (film surface) of the magnetic layer. In this case, eachmagnetic layer 11, 12 has magnetization which is substantially parallelto the layer surface of the magnetic layer 11, 12. The direction ofmagnetization of the magnetic layer 11, 12 having in-plane magneticanisotropy is perpendicular to the direction (Z direction) ofarrangement of the magnetic layers 11 and 12.

For example, when the magnetic layer 11, 12 has perpendicular magneticanisotropy, the magnetization easy axis direction of the magnetic layer11, 12 having perpendicular magnetic anisotropy is substantiallyperpendicular to the layer surface (film surface) of the magnetic layer.In this case, each magnetic layer 11, 12 has magnetization which issubstantially perpendicular to the layer surface of the magnetic layer11, 12. The direction of magnetization of the magnetic layer 11, 12having perpendicular magnetic anisotropy is parallel to the direction (Zdirection) of arrangement of the magnetic layers 11 and 12.

The direction of magnetization of the magnetic layer 11 is changeable.The direction of magnetization of the magnetic layer 12 is unchangeable(in a fixed state). Hereinafter, the magnetic layer 11 with thechangeable magnetization direction is referred to as “storage layer”.Hereinafter, the magnetic layer 12 with the unchangeable magnetizationdirection (in the fixed state) is referred to “reference layer”. Notethat, in some cases, the storage layer 11 is referred to as “freelayer”, “magnetization free layer” or “magnetization changeable layer”.In some cases, the reference layer 12 is referred to as “pin layer”,“pinned layer”, “magnetization unchangeable layer” or “magnetizationfixed layer”.

The magnetization direction of the storage layer 11 and themagnetization direction of the magnetic layer 59 change in interlockwith each other. For example, as regards the magnetization easy axisdirection of each layer, the magnetization direction of the storagelayer 11 is identical to the magnetization direction of the magneticlayer 59.

Note that the magnetic layer 59 may be used as a storage layer of theMTJ element 10. In this case, the nonmagnetic layer 13 is provided onthe magnetic layer 59 such that the nonmagnetic layer 13 is in directcontact with the magnetic layer 59, without the magnetic layer 11 beingdisposed.

In the present embodiment, the wording “the magnetization direction ofthe reference layer (magnetic layer) is unchangeable” or “themagnetization direction of the reference layer (magnetic layer) is inthe fixed state” means that, when current, voltage or magnetic energy(e.g. magnetic field), with which the magnetization direction of thestorage layer changes, is supplied to the magnetoresistive effectelement 10, the magnetization direction of the reference layer does notchange before and after the supply of the current, voltage or magneticenergy.

The switching element 20 is provided above the MTJ element 10 in the Zdirection. The switching element 20 is electrically connected to the MTJelement 10 via, for example, a contact plug CP1 (or a conductive layer).The switching element 20 may be directly connected to the MTJ element10, without another member being interposed.

The switching element 20 includes, for example, two electrodes 21 and 22and a switching layer 23. The switching layer 23 is provided between thetwo electrodes 21 and 22. The electrode 21 is provided on the contactplug CP1 in the Z direction. The switching layer 23 is provided on theelectrode 21 in the Z direction. The electrode 22 is provided on theswitching layer 23 in the Z direction. The material of the switchinglayer 23 is, for example, a transition metal oxide, or a chalcogenidecompound.

The switching element 20 switches an electrical connection between thememory cell unit MU and the bit line BL. As a result,activation/deactivation (selection/non-selection) of the memory cellunit MU can be controlled.

The resistance state of the switching layer 23 changes to a highresistance state or a low resistance state in accordance with a current(or a voltage) supplied to the layer 23.

Thereby, the switching element 20 is set in an ON state (a lowresistance state, a conductive state) when a current which is equal toor higher than a threshold current (ON current) of the switching element20 (or a voltage which is equal to or higher than a threshold voltage)is supplied to the memory cell unit MU. The switching element 20 is setin an OFF state (a high resistance state, a non-conductive state) when acurrent which is lower than the threshold current of the switchingelement 20 is supplied to the memory cell unit MU.

The switching element 20 in the OFF state electrically disconnects thememory cell unit MU from the bit line BL.

The switching element 20 in the ON state can pass current through thememory cell MC. The switching element 20 in the ON state supplies thememory cell unit MU with a current flowing from the bit line BL sidetoward the word line WL side, or a current flowing from the word line WLside toward the bit line BL side, in accordance with a potentialdifference between the bit line BL and the word line WL. In this manner,the switching element 20 is an element which can pass current throughthe memory cell unit MU in both directions.

A conductive layer 70 is provided between the magnetic member 50 and thesubstrate 9. The conductive layer 70 is provided on an insulating layer90 which covers the upper surface of the substrate 9. For example, theconductive layer 70 is buried in a trench in the insulating layer 90.The conductive layer 70 extends in the X direction. Note that a magneticlayer or a conductive layer may be provided between the conductive layer70 and the magnetic member 50.

The conductive layer 70 is used as the word line WL. The conductivelayer 70 functioning as the word line WL is electrically connected tothe row control circuit 110. The activation/deactivation(selection/non-selection) of the word line WL is controlled by the rowcontrol circuit 110.

A conductive layer 71 is provided above the switching element 20 in theZ direction. The conductive layer 71 is electrically connected to theswitching element 20 via a contact plug CP2. The conductive layer 71extends in the Y direction.

The conductive layer 71 is used as the bit line BL. The conductive layer71 functioning as the bit line BL is electrically connected to thecolumn control circuit 120. The activation/deactivation(selection/non-selection) of the bit line BL is controlled by the columncontrol circuit 120.

A conductive layer 75 is provided in an insulating layer 98 between themagnetic layer 59 and the bit line BL. The conductive layer 75neighbors, in the Y direction, the stacked body including thereproducing element 10 and switching element 20. The conductive layer 75extends in the X direction.

The conductive layer 75 is used as the write line FL. The conductivelayer 75 functioning as the write line FL is electrically connected to,for example, the row control circuit 110 and write circuit 140. Theactivation/deactivation of the write line 75 is controlled by the rowcontrol circuit 110. The supply of a write current PWR to the write lineFL is controlled by the write circuit 140.

For example, the domain wall memory including the memory cell unitillustrated in FIG. 3 and FIG. 4 functions as a domain wall shift memory(e.g. a shift register) of an LIFO (Last-in First-out) method.

As illustrated in FIG. 3 and FIG. 4, in the domain wall memory of thepresent embodiment, the dimension of the magnetic member 50 (e.g. thediameter of the cylindrical magnetic layer) in the direction (Xdirection or Y direction) parallel to the upper surface of the substrate9 cyclically varies in the Z direction. The magnetic member 50 isconstricted at predetermined intervals (cycles) in the Z direction.

Each memory cell MC includes a plurality of projection (convex) portions511 and 512 and a plurality of concave portions 521 and 522. Theprojection portions 511 and 512 and concave portions 521 and 522 are onecontinuous layer in the magnetic member 50. In the magnetic member 50,the projection portions 511 and 512 are arranged in the Z direction.

One memory cell MC includes a first projection portion 511 and a secondprojection portion 512. For example, in each memory cell MC, the secondprojection portion 512 is provided on the upper side (on the bit line BLside) of the first projection portion 511 in the Z direction.

The first projection portion 511 has a first dimension D1 in thedirection parallel to the upper surface of the substrate 9 (e.g. in atleast one of the X direction and Y direction). For example, thedimension D1 is a maximum dimension of the projection portion 511 in theX direction (or in the Y direction). The dimension D1 corresponds to thediameter of the magnetic member 50 at a position of the projectionportion 511. The projection portion 511 has a dimension L1 in the Zdirection.

The cross-sectional area of the projection portion 511 is maximum at theposition of the dimension D1.

The second projection portion 512 has a second dimension D2 in thedirection parallel to the upper surface of the substrate 9 (e.g. in atleast one of the X direction and Y direction). For example, thedimension D2 is a maximum dimension of the projection portion 512 in theX direction (or in the Y direction). The dimension D2 corresponds to thediameter of the magnetic member 50 at a position of the projectionportion 512. The dimension D2 is less than the dimension D1. Theprojection portion 512 has a dimension L2 in the Z direction. Forexample, the dimension L2 is substantially equal to the dimension L1.

The cross-sectional area of the projection portion 512 is maximum at theposition of the dimension D2.

The volume of a magnetic portion (magnetic member), which constitutesthe first projection portion 511, is greater than the volume of amagnetic portion which constitutes the second projection portion 512.

For example, each projection portion 511, 512 has a hexagonalcross-sectional shape as viewed in the X direction (or Y direction).

Hereinafter, the projection portion 511 is also referred as “largeprojection portion 511”, and the projection portion 512 is also referredto as “small projection portion 512”.

The concave portion 521 is provided between the first projection portion(large projection portion) 511 and the second projection portion (smallprojection portion) 512. The concave portion 521 has a third dimensionD3 in the direction parallel to the upper surface of the substrate 9.The dimension D3 is less than the dimension D1 and dimension D2. Thedimension D3 corresponds to the diameter (e.g. a minimum diameter of themagnetic member) of the magnetic member 50 at a position of the concaveportion 521. The concave portion 521 has a dimension L3 in the Zdirection. For example, the dimension L3 is less than the dimension L1and dimension L2.

For example, a dimension (distance) DB between an apex portion of theprojection portion 511 and a bottom portion of the concave portion 521in the X direction (or Y direction) is defined as a depth of aconstriction between the projection portion 511 and the concave portion521. Note that the apex portion of the projection portion 511 is aportion of the projection portion 511, which has the maximum dimensionD1. The bottom portion of the concave portion 521 is a portion havingthe dimension D3 of the concave portion 521.

For example, a dimension (distance) DA between the projection portion512 and the concave portion 521 in the X direction (or Y direction) isdefined as a depth of a constriction between an apex portion of theprojection portion 512 and a bottom portion of the concave portion 521.Note that the apex portion of the projection portion 512 is a portion ofthe projection portion 512, which has the maximum dimension D2.

The projection portions 511 and 512 and the concave portion 521 areprovided between two concaves portions 522 (522 a, 522 b) in the Zdirection.

One concave portion 522 a is provided on one end side in the Z directionof the cell region 510. The other concave portion 522 b is provided onthe other end side in the Z direction of the cell region 510. Eachconcave portion 522 is provided between two mutually neighboring memorycells MC in the Z direction.

The concave portion 522 has a dimension D4 in the direction (e.g. atleast one of the X direction and Y direction) parallel to the uppersurface of the substrate 9. The dimension D4 corresponds to the diameter(e.g. minimum diameter) of the magnetic member 50 at a position of theconcave portion 522.

The dimension D4 is less than the dimension D1 and dimension D2. Forexample, the dimension D4 is substantially equal to the dimension D3.The concave portion 521 has a dimension L4 in the Z direction. Forexample, the dimension L4 is substantially equal to the dimension L3.

In the present embodiment, a domain wall is retained in the concaveportion 522 in accordance with the state of magnetization (magneticdomain) of mutually neighboring memory cells MC (projection portions 511and 512). Hereinafter, the concave portion 522 is also referred to as“domain wall retention portion 522” (or “domain wall existence region522”).

In two mutually neighboring memory cells MC, the concave portion 522between one memory cell MC and the other memory cell MC functions as adomain wall retention portion of the one memory cell MC. One end of theother memory cell MC functions as a domain wall retention portion of theone memory cell MC, and the other end of the other memory cell MCfunctions as a domain wall retention portion of the other memory cellMC.

In this manner, each concave portion 522 is shared by two memory cellsMC which neighbor in the Z direction. Each concave portion 522 is usedas the domain wall retention portion of one of the two memory cells MCwhich share the concave portion 522. The concave portion 522 is disposedat a boundary of the mutually neighboring memory cells MC.

One projection portion 511, one projection portion 512 and one concaveportion 521 are, at least, provided in one cell region 510.

A structure including at least the projection portions 511 and 512 andconcave portion 521 forms a region of one cycle in the magnetic member50 having a cyclic constriction structure. The structure of one cycle isused as one memory cell MC.

In the present embodiment, each of the projection portions 511 and 512includes a portion having a certain dimension in the magnetic member 50,and a region of a certain size centering on the portion having thisdimension. In the present embodiment, each of the concave portions(hereinafter, also referred to as “constriction portions” or“constriction regions”) 521 and 522 includes a portion having a certaindimension in the magnetic member 50, and a region of a certain sizecentering on the portion having this dimension.

In the present embodiment, the dimensions of the respective portions inthe cylindrical magnetic member 50 are set with reference to a plane onthe outer peripheral side (outer wall side) of the magnetic member 50.However, if the large/small relationship of dimensions of the respectiveportions of the magnetic member in the present embodiment is satisfied,the dimensions of the respective portions may be defined with referenceto a plane on the inner peripheral side (inner wall side) of themagnetic member 50.

Note that the magnetic member 50 may include a portion of a fixeddimension (a region with an invariable dimension) in a directioncrossing the direction of motion of the domain wall in the projectionportion 511, 512 and the concave portion 521, 522.

In the domain wall memory 1 of the present embodiment, the shift of datain the memory cell unit MU is executed by a shift operation on thedomain wall in the magnetic member 50.

As will be described later, in the domain wall memory of the presentembodiment, a domain wall retained in a certain memory cell MC is moved(shifted) to another memory cell MC by a shift pulse (e.g. a currentpulse) supplied to the magnetic member 50. In one example of theoperation sequence of the domain wall memory, the domain wall is shiftedby one cycle (one memory cell) by one-time supply of a shift pulse. Inaccordance with the shift of a domain wall DW between memory cells MC,magnetic domains in the memory cells MC move.

In the domain wall memory of the present embodiment, the concave portion(constriction portion) 521 is provided in each memory cell MC.

In the memory cell MC, the large projection portion 511 and smallprojection portion 512 are arranged in the extending direction of themagnetic member 50, with the concave portion 521 being interposed. Thedimension D1 of the large projection portion 511 in the paralleldirection to the upper surface of the substrate 9 is greater than thedimension D2 of the small projection portion 512 in the paralleldirection to the upper surface of the substrate 9. For example, in thememory cell MC, with respect to the direction of motion of the domainwall, the large projection portion 511 is located on thesource-of-motion side of the domain wall, and the small projectionportion 512 is located on the destination-of-motion side of the domainwall.

For example, a domain wall exists in a concave portion 522 a on one sideof a certain cell region 510 (a domain wall retention portion 522 a of acertain memory cell).

In the domain wall memory of the present embodiment, this domain wall isshifted into a concave portion 522 b on the other side of the cellregion 510 (a domain wall retention portion 522 b of the neighboringcell) via the concave portion 521 (and projection portions 511 and 512),by using a shift pulse which includes two pulses.

Note that, in the present embodiment, there is a case in which thedomain wall is located in the concave portion 521 in a temporary stateat the time of the shift operation (the shift of data).

The volume of the first projection portion (large projection portion)511 having the first dimension D1 is greater than the volume of thesecond projection portion (small projection portion) 512 having thesecond dimension D2. Thus, the energy for the domain wall to move in thefirst projection portion 511 is greater than the energy for the domainwall to move in the second projection portion 512.

In the magnetic member 50, compared to the second portion (smallprojection portion) 512, the first projection portion 511 functions as astopper (barrier) of motion of the domain wall, with respect to theshift current of a certain current value at the time of the shiftoperation.

Thereby, the domain wall memory of the present embodiment can suppressexcessive motion of the domain wall between the memory cells. Therefore,the domain wall memory of the present embodiment can decrease an errorof the position of the domain wall which is moved by the shift operationto a target position.

Therefore, the domain wall memory of the present embodiment can suppressa shift error of the domain wall.

Note that, in the domain wall memory of the present embodiment, each ofthe projection portion 511 and projection portion 512 in the magneticmember 50 has a substantially symmetric shape with respect to thedirection of motion of the domain wall (here, in the Z direction), withthe position having the maximum dimension of each portion 511, 512 beingset as the center. In addition, in the present embodiment, theprojection portions 511 and projection portions 512 are alternatelyarranged in the magnetic member 50 in the direction of motion of thedomain wall.

Therefore, in the domain wall memory of the present embodiment, when thedomain wall is shifted from one end side (e.g. word line side) of themagnetic member 50 to the other end side (e.g. bit line side) of themagnetic member 50, or when the domain wall is shifted from the otherend side of the magnetic member 50 to the one end side of the magneticmember 50, in response to a predetermined shift pulse which is supplied,it is possible to suppress a variance in shift amount (motion distance)of the domain wall due to asymmetry in shape of each projection portion.

Furthermore, in the domain wall memory of the present embodiment, thepulse shape of the shift pulse in the case where the domain wall ismoved from the one end side of the magnetic member 50 to the other endside (e.g. bit line side) of the magnetic member 50 can be madesubstantially identical to the pulse shape of the shift pulse in thecase where the domain wall is moved from the other end side of themagnetic member 50 to the one end side of the magnetic member 50.

(b) Manufacturing Method

Referring to FIG. 5 to FIG. 9, a manufacturing method of the magneticmemory of the present embodiment will be described.

FIG. 5 to FIG. 9 are cross-sectional process views illustratingfabrication steps of the manufacturing method of the magnetic memory(e.g. domain wall memory) of the present embodiment.

As illustrated in FIG. 5, a plurality of layers 911, 912, 913 and 915are formed on the upper surface of the substrate 9 at predeterminedcycles (arrangement). For example, before forming the layers 911, 912,913 and 915, interconnects (not shown) having a predetermined patternare formed in an insulating layer (not shown) on the substrate 9 or onan insulating layer on the substrate 9.

For example, a hafnium oxide layer (also referred to as “hafnia layer”)(HfO₂ layer) 911 is formed on the substrate 9. A silicon oxide layer(SiO₂ layer) 912 is formed above the HfO₂ layer 911 in the Z direction.Further, a hafnium oxide layer 911 is formed above silicon oxide layer912. Besides, a hafnium silicon oxide layer (also referred to as“hafnium silicate layer”) (HfSiO₄ layer) 913 is formed above the hafniumoxide layer 911 in the Z direction.

In addition, a HfO₂ layer 911 is formed on the HfSiO₄ layer 913.Further, a SiO₂ layer 912 is formed above the HfSiO₄ layer 913 via theHfO₂ layer 911. In this manner, the SiO₂ layer 912 and the HfSiO₄ layer913 are alternately formed in the Z direction, with the HfO₂ layer 911being interposed.

In the present embodiment, the layers 911, 912 and 913 are formed suchthat the concentrations of constituent elements in the layers 911, 912and 913 vary in the Z direction.

Thus, intermediate layers (hereinafter, also referred to as“concentration modulation layers”) 915 are provided between the layers911, 912 and 913. The intermediate layer 915 is a region where theconcentrations of constituent elements in layers gradually vary from acentral portion of one layer toward a central portion of the otherlayer. Between two layers, the concentration of a certain constituentelement of one layer has a maximum value at a central portion of the onelayer, and gradually decreases in the intermediate layer 915 toward acentral portion of the other layer.

FIG. 6 is a schematic view for explaining variations of theconcentrations of constituent elements in a stacked body.

FIG. 6 illustrates a variation (line CON-Hf) of the concentration of Hfand a variation (line CON-Si) of the concentration of Si in a stackedbody 900.

As illustrated in FIG. 6, the concentration of Hf is highest in acentral portion of the HfO₂ layer 911 and gradually lowers toward theSiO₂ layer 912. The concentration of Si is highest in a central portionof the SiO₂ layer 912 and gradually lowers toward the HfO₂ layer 911.

From the HfO₂ layer 911 toward the intermediate layer 915, the Hfelement is replaced with the Si element. From the SiO₂ layer 912 towardthe intermediate layer 915, the Si element is replaced with the Hfelement.

The region 915 between the central portion of the HfO₂ layer 911 and thecentral portion of the SiO₂ layer 912 becomes an oxide region includingHf and Si. As a result, the intermediate layer 915 is formed between theHfO₂ layer 911 and the SiO₂ layer 912. The intermediate layer 915 is a(HfO₂)_(x)(SiO₂)_(1-x) layer (0<x<1). The Hf concentration in theintermediate layer 915 is lower than the Hf concentration in the centralportion of the HfO₂ layer 911, and is higher than the Hf concentrationin the central portion of the SiO₂ layer 912. The Si concentration inthe intermediate layer 915 is lower than the Si concentration in thecentral portion of the SiO₂ layer 912, and is higher than the Siconcentration in the HfO₂ layer 911.

In accordance with the variation of the concentrations of theconstituent elements in the Z direction, the properties of the layers911, 912 and 915 vary in the Z direction.

Note that when the Hf concentration and Si concentration vary withgradients between the layers in the stacked body 900, there may be acase in which boundaries (interfaces) between the layers 911, 912 and915 are not clear as in FIG. 6.

Between the HfO₂ layer 911 and HfSiO₄ layer 913, the Hf element isreplaced with the Si element from the HfO₂ layer 911 toward theintermediate layer 915. The Si element is replaced with the Hf elementfrom the HfSiO₄ layer 913 toward the intermediate layer 915.

Between the central portion of the HfO₂ layer 911 and the centralportion of the HfSiO₂ layer 913, the Hf concentration of theintermediate layer 915 is lower than the Hf concentration in the centralportion of the HfO₂ layer 911 and is higher than the concentration inthe central portion of the HfSiO₄ layer 913. The Si concentration of theintermediate layer 915 is lower than the concentration in the centralportion of the HfSiO₄ layer 913.

In accordance with the variation of the concentrations of theconstituent elements in the Z direction, the properties of the layers911, 913 and 915 vary in the Z direction.

Note that when the Hf concentration and Si concentration in the layersvary with gradients between the layers in the stacked body 900, theremay be a case in which boundaries (interfaces) between the layers 911,913 and 915 are not clear.

In this manner, the HfO₂ layers (HfO₂ regions) 911, SiO₂ layers (SiO₂regions) 912, HfSiO₄ layers (HfSiO₄ regions) 913 and intermediate layers((HfO₂)_(x)(SiO₂)_(1-x) regions) 915 are formed in the stacked body 900such that the concentration distribution of Hf and the concentrationdistribution of Si in the stacked body 900 vary with gradients in the Zdirection.

In the present embodiment, the example is illustrated in which thestacked body 900 is formed by using the layers including Hf and thelayers including Si. However, as materials of the layers that form thestacked body 900, use may be made of other insulators, for example,oxynitrides, silicates and aluminates, such as a nitride of silicon(also referred to as “silicon nitride” (SiN), silicon oxynitride (SiON),zirconium-silicon oxide (zirconium silicate) (ZrSiO), hafnium-aluminumoxide (hafnium aluminate) (HfAlO), and hafnium-silicon oxynitride(HfSiON).

As illustrated in FIG. 7, a hole 990 is formed in the stacked body 900by lithography and anisotropic etching (e.g. reactive etching). The hole990 extends in the Z direction in the stacked body 900. A bottom portionof the hole 990 reaches the upper surface of the substrate 9.

Side surfaces of the layers 911, 912, 913 and 915 are exposed in thehole 990. Interconnects (not shown) on the substrate 9 are exposed viathe hole 990. Note that each layer has a substantially uniform thicknessin the layer, and layer surface of each layer is parallel to the uppersurface of the substrate.

For example, the plan-view shape of the hole 990 as viewed in the Zdirection is circular (or elliptic). In this case, the hole 990 has acylindrical structure. Note that the plan-view shape of the hole 990 asviewed in the Z direction may be rectangular.

Thereafter, isotropic etching (e.g. wet etching) is performed on thestacked body 900.

As illustrated in FIG. 8, the side surfaces of the layers 911, 912, 913and 915 in the hole 990 retreat in a parallel direction to the uppersurface of the substrate 9 by the isotropic etching.

The condition for the isotropic etching is set such that a large etchingselectivity can be secured between the layer 911 including hafnium andthe layer 912 including silicon.

For example, wet etching is performed by using hydrofluoric acid as anetching solution.

In this case, the etching amount (etching rate) of each layer 911, 912,913 and 915 varies depending on the Si concentration in the layer. Thus,the etching amount of the SiO₂ layer 912 is greater than the etchingamount of the HfO₂ layer 911. The etching amount of each of the HfSiO₄layer 913 and the intermediate layer 915 is less than the etching amountof the SiO₂ layer and is greater than the etching amount of the HfO₂layer.

Therefore, in the hole 990 in the stacked body 900, the side surface ofthe SiO₂ layer 912, the side surface of the HfSiO₄ layer 913 and theside surface of the intermediate layer 915 retreat in the paralleldirection to the upper surface of the substrate 9, compared to the sidesurface of the HfO₂ layer 911.

Thereby, a recess 941 is formed at the position of the SiO₂ layer 912(and intermediate layer 915), and a recess 942 is formed at the positionof the HfSiO₄ layer 913 (and intermediate layer 915).

A depth G1 of the recess 941 in the parallel direction to the uppersurfaced of the substrate 9 is greater than a depth G2 of the recess 942in the parallel direction to the upper surface of the substrate 9.

In this manner, the recesses 941 and 942 with different depths areformed in the stacked body 900. As a result, a hole having a cyclicallyconstricted structure in the Z direction (a hole having an openingdimension varying in the Z direction) is formed in the stacked body 900.

For example, as described above, when the SiO₂ layer, HfO₂ layer andHfSiO₂ layer are formed such that the Si concentrations and Hfconcentrations thereof vary with gradients, the cross-sectional shape ofthe recess 941, 942 becomes triangular.

As illustrated in FIG. 9, in the hole 990, a magnetic layer 500 isformed on a side surface of the stacked body 900. The magnetic layer 500covers the side surfaces of the layers 911, 912, 913 and 915 of thestacked body 900 in the hole 990, along the shapes of the recesses 941and 942.

Thereby, the magnetic member 50 extending in the Z direction is formedin the stacked body 900. The magnetic member 50 includes the projectionportions 511 and 512 and the concave portions 521 and 522. The magneticmember 50 has a cylindrical shape.

The projection portion 511 of the magnetic member 50 is formed in therecess 941. The projection portion 512 is formed in the recess 942. Theconcave portion 521, 522 is formed in a region between the recess 941and recess 942 in the Z direction.

The magnetic member 50 is constricted in accordance with the shapes ofthe recesses 941 and 942. The dimension in the Y direction of themagnetic member 50 at the position of the recess 941 is greater than thedimension in the Y direction of the magnetic member 50 at the positionof the recess 942.

As described above, the magnetic member 50 having the constrictionstructure is formed above the substrate 9.

Thereafter, the reproducing element, switching element and variousinterconnects are formed above the magnetic member 50. Thereby, thememory cell unit in the domain wall memory of the present embodiment isformed.

By the above manufacturing method, the domain wall memory of the presentembodiment is formed.

Note that the hole with the constriction structure, which forms themagnetic member 50, may be formed by using anodic oxidation of a metal(e.g. aluminum).

(c) Operation Example

Referring to FIG. 10 to FIG. 19, an operation example of the domain wallmemory of the present embodiment will be described.

(c-1) Outline of Shift Operation

FIG. 10 is a schematic diagram for explaining a shift operation of thedomain wall memory of the present embodiment.

As illustrated in part (a) of FIG. 10, before supplying a shift pulse SPthat is used in a shift operation, the memory cells MC (MC<1> to MC<5>)have magnetizations (magnetic domains) MM1, MM2, MM3, MM4 and MM5corresponding to stored data.

In the example of FIG. 10, the magnetic member 50 has perpendicularmagnetic anisotropy. For example, a magnetization, which is directed tothe outside (outer peripheral side) of the cylindrical magnetic member50, is associated with first data (one of “0” data and “1” data), and amagnetization, which is directed to the inside (center axis side) of thecylindrical magnetic member 50, is associated with second data (theother of “0” data and “1” data).

When the magnetization directions of two mutually neighboring memorycells MC are different (i.e. when mutually neighboring memory cells MCstore different data), a domain wall DW is disposed in the concaveportion 522 between the mutually neighboring memory cells.

The cell regions (magnetic portions) 510 corresponding to two mutuallyneighboring memory cells MC with different magnetization directions havemagnetic domains MD (MD1, MD2, MD3, and MD4) separated by the domainwall DW.

When the magnetization directions of two mutually neighboring memorycells MC are identical (i.e. when mutually neighboring memory cells MCstore identical data), a domain wall DW is not formed in the concaveportion 522 between the two cell regions 510 corresponding to themutually neighboring memory cells MC.

The mutually neighboring cell regions 510 with the identicalmagnetization direction have one magnetic domain MD which is continuousbetween the two cell regions 510. Note that there is a case in which onemagnetic domain MD is formed to include three or more consecutive cellregions 510, depending on the arrangement of “1” and “0” of data storedin the memory cell unit.

For example, when the memory cells MC<2> and MC<3> store identical data(magnetization MM2 and MM3), one magnetic domain MD2 is formed toinclude two consecutive cell regions 510 in which the memory cells MC<2>and MC<3> are provided.

For example, when the data (magnetization MM4) of the memory cell MC<4>is different from the data (magnetization MM3) of the memory cell MC<3>and the data (magnetization MM5) of the memory cell MC<5>, domain wallsDW are formed between the cell region 510, in which the memory cellMC<4> is provided, and the cell region 510, in which the memory cellMC<3> is provided, and between the cell region 510, in which the memorycell MC<4> is provided, and the cell region 510, in which the memorycell MC<5> is provided. Thus, magnetic domains MD2, MD3 and MD4, whichare separated by the domain walls DW, are formed in the cell region 510of the memory cell MC<3>, the cell region 510 of the memory cell MC<4>and the cell region 510 of the memory cell MC<5>, respectively.

The magnetic domain MD1 of the memory cell MC<1> is separated by thedomain wall DW from the magnetic domain MD2 in the cell regions 510 ofthe memory cells MC<2> and MC<3>.

For example, in the magnetic member in the magnetic domain state of theexample of part (a) of FIG. 10, a shift pulse SP is supplied to themagnetic member 50. Note that the direction of motion of electrons (e⁻)is opposite to the direction of motion of the shift pulse SP that is anelectric current.

As illustrated in part (b) of FIG. 10, at the time of the shiftoperation, the shift pulse SP flows in the magnetic member 50. In thepresent example, electrons (e⁻) move in a direction from the memory cellMC<1> toward the memory cell MC<5>.

When the shift pulse SP is supplied to the magnetic member 50, alldomain walls DW in the magnetic member 50 are substantiallysimultaneously moved in the magnetic member 50 by the shift pulse SP. Inthe present example, the direction of motion of the domain wall DWagrees with the direction of motion of electrons.

For example, the motion of the domain wall DW in the shift operation isdue to STT (Spin transfer torque) and/or SOT (Spin orbit torque)occurring in the magnetic member.

In accordance with the motion of the domain wall DW, the magnetization(magnetic domain) MD in the cell region 510 moves.

Thereby, data shifts in the magnetic member 50 in the memory cell unitMU. For example, the magnetic domain MD1 of the cell region 510 in thememory cell MC<1> prior to the shift operation moves to the cell region510 in the memory cell MC<2> by the shift operation. A magnetic domainMD0 (magnetization MM0) of a neighboring memory cell moves to the cellregion 510 in the memory cell MC<1>.

In this manner, the magnetic domain MD is shifted by one memory cell (byone bit) by the motion of the domain wall DW.

In the present embodiment, the shift operation (motion of the domainwall/magnetic domain) is executed by the supply of a pulse (e.g. acurrent pulse) to the magnetic member 50 in such a manner that thedomain wall DW is located in the concave portion 522 of the magneticmember 50 of the constriction structure. At the time of the shiftoperation, the domain wall DW moves in two steps to the concave portion522 via the concave portion 521.

In the magnetic member 50 of the constriction structure, the domain wallDW can exist more stably in the magnetic region with a small volume(e.g. the concave portion in this embodiment), than in the magneticregion with a large volume (e.g. the projection portion in thisembodiment).

Therefore, there is a tendency that the domain wall DW, which is movedby the shift operation, is located in the concave portion 521, 522 (andin a region near the concave portion 521, 522), compared to theprojection portion 511, 512.

As a result, when the magnetic member 50 of the constriction structureis used, the controllability of the position of the domain wall DW inthe magnetic member 50 can be enhanced.

As will be described below, in the domain wall memory of the presentembodiment, the shift pulse SP includes a plurality of pulses. Thereby,the domain wall DW is moved in the memory cell unit MU such that thedomain wall DW is located in the concave portion (domain wall retentionportion) 522 of the memory cell MC via the concave portion 521.

In the present embodiment, an example is illustrated in which the domainwall moves in the magnetic member along the direction of motion ofelectrons by the shift pulse SP at the time of the shift operation.

Note that the direction of motion of the domain wall at the time of thepulse operation can be controlled by the material of the magneticmember, the material of a conductive member stacked on the magneticmember, the position of the conductive member relative to the magneticmember, and manufacturing conditions. When a conductive member isstacked on the magnetic member, for example, platinum (Pt), tungsten(W), tantalum (Ta), etc. can be used as the material of the conductivemember. However, the materials of the conductive member are not limitedto these.

In the present embodiment, the magnetic member 50 may have in-planemagnetic anisotropy. In this case, the magnetization easy axis directionof the magnetic member 50 is parallel to the Z direction. When themagnetic member 50 has the in-plane magnetic anisotropy, for example,magnetic layers with in-plane magnetic anisotropy may be used for themagnetic layers 11 and 12 of the MTJ element 10.

(c-2) Shift Pulse

FIG. 11 is a waveform diagram illustrating a shift pulse used in theshift operation of the domain wall memory of the present embodiment. Theabscissa axis of FIG. 11 corresponds to time, and the ordinate axis ofFIG. 11 corresponds to an absolute value of a current value.

As illustrated in FIG. 11, in the shift operation of the domain wallmemory of the present embodiment, the shift pulse SP is supplied duringa period (hereinafter referred to as “shift operation period”) TS of theshift operation.

The shift pulse (hereinafter, also referred to as “shift current”) SPis, for example, a current pulse.

In the present embodiment, the shift current SP includes a first pulseP1 and a second pulse P2. By the pulses P1 and P2 which are supplied,the energy for moving the domain wall is applied to the domain wall inthe magnetic member.

The first pulse P1 has a current value ia. The first pulse P1 has apulse width t_(p1). The second pulse P2 has a current value ib. Thesecond pulse P2 has a pulse width t_(p2).

The current value ia is equal to or greater than a current value iax.The current value iax is a current value of a critical current formoving the domain wall DW from the concave portion 522 to the concaveportion 521 via the projection portion 511.

The current value ib is equal to or greater than a current value ibx.The current value ibx is a current value of a critical current formoving the domain wall DW from the concave portion 521 to the concaveportion 522 via the projection portion 512.

The current values iax and ibx are higher than a threshold (hereinafter,also referred to as “domain wall shift threshold”) ith of motion (shift)of the domain wall in the magnetic member 50 of the constrictionstructure.

The domain wall shift threshold in the magnetic member 50 of theconstriction structure is indicative of a current value at which thedomain wall begins to move (shift) by the function of energy due to SOTand/or STT by current (electrons).

For example, the domain wall shift threshold ith in the magnetic member50 of the constriction structure can be calculated by a product of aminimum value of a cross-sectional area (e.g. a cross-sectional area ofthe concave portion 522 as viewed in the Z direction) of the cell region510 in the Z direction and a critical current density for the shift ofthe domain wall. The critical current density for the shift of thedomain wall in the magnetic member varies depending on the material ofthe magnetic member and the structure of the magnetic member.

Here, it is assumed that the cross-sectional area at the position of theconcave portion 522 (or concave portion 521) in the magnetic member 50is a minimum value of the cross-sectional area of the cell region 510(magnetic member 50). When a current of the current value ith issupplied to the magnetic member, the domain wall in the concave portion522 shifts toward the projection portion 511 (or projection portion512). However, since the current value ith is less than the currentvalues iax and ibx, the domain wall cannot move beyond the apex portionof the projection portion 511 even if the domain wall shifts to a regionbetween the apex portion of the projection portion 511 (a portion with amaximum cross-sectional area of the projection portion 511) and theconcave portion 522. Therefore, before and after the supply of thecurrent of the current value ith to the magnetic member, the position ofthe domain wall DW in the concave portion 522 does not substantiallychange. When the cross-sectional area of the concave portion 521 isgreater than the cross-sectional area of the concave portion 522, evenif the current of the current value ith is supplied to the magneticmember 50, a domain wall that may exist in the concave portion 521 doesnot move (shift).

When the current value of the current supplied to the magnetic member 50is less than the domain wall shift threshold ith, no motion (shift) ofthe domain wall occurs in the magnetic member 50.

For example, the magnitude of the pulse width t_(p2) is substantiallyequal to the magnitude of the pulse width t_(p1). However, the magnitudeof the pulse width t_(p2) may be different from the magnitude of thepulse width t_(p1).

For example, each pulse width (t_(p1) and t_(p2)) is a value based on afull width at half maximum of each pulse (P1 and P2). However, if thestandard for defining the magnitude of the pulse width is common to twopulses, the pulse width t_(p1) and t_(p2) may be defined based on astandard other than the full width at half maximum.

In the present embodiment, as regards the pulse P1 of the shift currentSP, the pulse width t_(p1) of the pulse P1 has a magnitude based on aperiod during which the domain wall in the domain wall retention portion522 of a certain memory cell moves into the projection portion 512 (orconcave portion 521, 522) of a memory cell MC neighboring by one cycle,when the shift current of a certain current value ia is supplied.

As regards the pulse P2 of the shift current SP, the pulse width t_(p2)of the pulse P2 has a value based on a period during which the domainwall in the domain wall retention portion 521 moves to the concaveportion (domain wall retention portion) 522 of the memory cell MC (or aregion between the apex portion of the projection portion 512 of acertain memory cell MC<k> and the apex portion of the projection portion511 of another memory cell MC<k+1>).

Note that the apex portion of the projection portion 511 corresponds toa portion with the maximum dimension D1 in the projection portion 511.The apex portion of the projection portion 512 corresponds to a portionwith the maximum dimension D2 in the projection portion 512.

For example, the pulse width (the time of motion of the domain wall DW)t_(p1) of the pulse P1 is set in accordance with a time for the motionover a dimension which is equal to or greater than the dimension L1 inthe Z direction from the concave portion (the domain wall retentionportion of the memory cell MC) 522 to the concave portion 521 in thedirection of motion of the domain wall (the dimension of the projectionportion 511 in the direction of motion of the domain wall DW), and whichis less than a dimension “L1+L2” from the concave portion 522 to theconcave portion 522 in the direction of motion of the domain wall, whenthe shift current of a certain current value is ia supplied. Note thatthe dimension L3 (L4) in the Z direction of the concave portion 521(522) is set to be sufficiently smaller than the dimension L1 (L2).Here, the dimensions L3 and L4 are approximated to zero.

It is preferable that the distance of motion of the domain wall at atime when the pulse P1 of the pulse width t_(p1) is supplied is a valueapproximated to a distance to a substantially middle position betweentwo projection portions 511 which neighbor in the direction of motion ofthe domain wall.

For example, it is preferable that when the shape of a projectionportion 511 is configured to be symmetric in the left-and-rightdirection (symmetric in the up-and-down direction) with respect to thedirection of motion of the domain wall, the distance of motion of thedomain wall at the time of supply of the pulse P1 is approximated to adistance “L1+L2/2” [to a middle position between the position of L1/2 ofthe projection portion 511 and the position (L1/2+L1+L2) of a projectionportion 511 which neighbors in the direction of motion of the domainwall, with the projection portion 512 being interposed].

The velocity of motion of the domain wall DW between the concaveportions 522 and 521 can be calculated by using the time of motion ofthe domain wall DW (the pulse width of the pulse) and the distance L1between the two concave portions 522 and 521. Note that, here, theactual length of the magnetic portion, which functions as the projectionportion 511 (or projection portion 512), is approximated to thedimension L1 in the Z direction of the projection portion 511 (or thedimension L2 in the Z direction of the projection portion 512).

Preferably, the current values ia and ib have a relationship of amathematical expression (eq1) below.ia>A _(L) Jc>ib>A _(S) Jc  (eq1)

Here, the maximum value of the cross-sectional area of the projectionportion (large projection portion) 511 is indicated by “A_(L)”, and themaximum value of the cross-sectional area of the projection portion(small projection portion) 512 is indicated by “A_(S)”. In addition, thecritical current density for moving the domain wall is indicated by“Jc”.

In the expression (eq1), “A_(L)Jc” corresponds to the current value iax,and “A_(S)Jc” corresponds to the current value ibx.

For example, a motion velocity v_(DW) of the domain wall can beexpressed by the following equation (eq2).v _(DW) =C×((J/Jc)²−1)^(1/2)  (eq2)

Here, “C” is a proportionality factor, and “J” is a current density ofcurrent used in the shift. The current density in the pulse P1 of thecurrent value ia is indicated by “Ja”. The current density in the pulseP2 of the current value ib is indicated by “Jb”.

At a time when a current Iz with a certain current value is beingsupplied to the magnetic member 50, the current density J is expressedby the following equation (eq3).J=Iz/A(z)  (eq3)

Here, “A(z)” is indicative of a cross-sectional area at a position (z)in the Z direction in the magnetic member 50. Note that the currentvalue of the pulse current Iz is constant without depending on theposition in the magnetic member 50.

The motion distance “L” of the domain wall is expressed as follows.L=v _(DW) ×t _(p) =C×((Iz/(A(z)×Jc))²−1)^(1/2) ×tp

Note that “tp” is the pulse width of the current Iz.

In this manner, the motion distance L of the domain wall is controlledin accordance with the current value of the pulses P1 and P2, whichserves as the current Iz, and the pulse width tp of the pulses P1 andP2.

In the present embodiment, as regards the pulse P2 of the shift currentSP, when the pulse P2 of the current value ib is supplied to themagnetic member 50, the magnitude of the current ib (and the magnitudeof the pulse width t_(p2)) is set such that the domain wall DW in theconcave portion 521, 522 of a certain memory cell MC<k> does not shiftinto a neighboring memory cell MC<k+1>.

In the present embodiment, the two pulses P1 and P2 of the shift currentSP have mutually different current values ia and ib.

For example, a period (hereinafter, also referred to as “relaxationperiod”) t_(rx1) is provided between the first pulse P1 and the secondpulse P2. The relaxation period t_(rx1) corresponds to a time untilmagnetization enters an equilibrium state. In the relaxation periodt_(rx1) with the magnetization entering the equilibrium state, themagnetic state of the shifted domain wall DW stabilizes.

A certain period (relaxation period) t_(rx2) is provided from the stopof the supply of the second pulse P2 to the terminal end of the shiftoperation (the start of the next supply of the shift current SP). In therelaxation period t_(rx2) after the supply of the second pulse P2, themagnetic state of the domain wall moved by the pulse P2 is stabilized.

FIG. 12 is a waveform diagram illustrating a modification of the shiftcurrent of the domain wall memory of the present embodiment.

As illustrated in FIG. 12, if the current value of the shift current SPis less than the domain wall shift threshold ith, the current value ofthe shift current SP may have a value ic which is greater than 0, in theperiod (relaxation period) between the two pulses P1 and P2.

The current value ic is greater than 0 and less than the domain wallshift threshold ith.

In this case, the two pulses P1 and P2 of the shift current have acontinuous pulse shape with a current value of 0 or more.

The domain wall memory of the present embodiment can shift the domainwall, in two motion steps, to a predetermined position (target position)in the magnetic member 50 having the constriction structure, by theshift current SP including the two pulses P1 and P2 with differentcurrent values, as illustrated in FIG. 11 and FIG. 12.

(c-3) Mechanism

Referring to FIG. 13 to FIG. 17, a mechanism of the shift operation inthe domain wall memory of the present embodiment will be described.

FIG. 13 to FIG. 17 are schematic views illustrating states of motion ofthe domain wall at the time of the shift operation in the domain wallmemory of the present embodiment. FIG. 13 to FIG. 17 illustratedistributions of existence probability of the domain wall (DW) in themagnetic member. Note that FIG. 13 also illustrates, for the purpose ofclearer description, the transition of the variation of thecross-sectional area of the magnetic member in relation to the positionin the magnetic member of the constriction structure.

Note that the cross-sectional area at a certain position in the magneticmember has a correlation with the volume of the domain wall at thatposition in the magnetic member. Therefore, based on the width of thedomain wall and the cross-sectional area of the magnetic member inrelation to the position in the magnetic member, the magnitude of thevolume of the magnetic member in relation to the position in themagnetic member can equivalently be calculated.

In the example illustrated in FIG. 13, prior to the supply of the shiftcurrent, the domain wall DW is retained in a memory cell MC<k−1>. Thedomain wall DW is disposed in a concave portion 522<k<1> of the memorycell MC<k−1> or a region near the concave portion 522<k−1> with acertain existence probability Q0.

When the domain wall DW is moved from the memory cell MC<k−1> to amemory cell MC<k>, the shift current SP including two pulses P1 and P2is supplied to the magnetic member 50.

As illustrated in FIG. 14, the first pulse P1 having a current value ia(ia>iax) is supplied to the magnetic member 50. The pulse P1 has a pulsewidth t_(p1). Thereby, a current corresponding to the current value iaflows in the magnetic member 50 during a period corresponding to thepulse width t_(p1).

By the supplied pulse P1, the domain wall DW in the concave portion 522moves from the memory cell MC<k−1> into the neighboring memory cellMC<k>. For example, the domain wall DW moves along the direction ofmotion of electrons.

In the memory cell MC<k>, the domain wall DW moves into a projectionportion 512<k> via a projection portion 511<k> by the pulse P1.

Preferably, the current value ia and pulse width t_(p1) of the pulse P1are set such that the domain wall DW moves to an intermediate position(e.g. a position C1) between the projection portion 511<k> and aprojection portion 511<k+1>.

Due to a variance in motion amount of the domain wall DW with respect tothe supplied pulse P1 and a variance in magnetic characteristics ofrespective portions in the magnetic member 50, a distribution Q1 of theexistence probability of the domain wall DW in the region from theprojection portion 511<k> to the projection portion 511<k+1> is widerthan a distribution Q0. A standard deviation σ of the existenceprobability distribution of the domain wall and a motion distance L ofthe domain wall vary while keeping the relation of σ²/L substantiallyconstant, when a motion velocity v of the domain wall is assumed to beconstant.

After the supply of the pulse P1, the shift operation temporarily entersa standby state during a period (relaxation period) t_(rx1) from thestop of supply of the pulse P1 to the start of supply of the pulse P2.In the magnetic member 50, the magnetic state of the projection portion511, 512 and concave portion 521, 522 transitions into a relaxationstate (equilibrium state) by the stop of supply of the pulse P1.

As illustrated in FIG. 15, during the relaxation period t_(rx1) afterthe supply of the pulse P1, the moved domain wall moves to a portionwith a smaller volume (a portion with a smaller dimension) in themagnetic member 50 from the portion where the domain wall currentlyexists, such that the domain wall enters a stabler energy state.

Therefore, domain walls DWa and DWb in the memory cell MC<k> shift fromthe projection portion 512<k> to concave portion 521<k> or from theprojection portion 512<k> to concave portion 522<k>.

As a result, during the relaxation period t_(rx1), the existenceprobability (distributions Q2 a and Q2 b) of the domain walls DWa andDWb in the memory cell MC<k> increases in a region near the boundarybetween the projection portion 512<k> and concave portion 521<k> or in aregion near the boundary between the projection portion 512<k> andconcave portion 522<k>.

As illustrated in FIG. 16, after the passage of the relaxation periodt_(rx1) the pulse P2 having a current value ib (iax>ib>ibx) is suppliedto the magnetic member 50. The current value ib of the pulse P2 is setto a current value which is equal to or greater than such a currentvalue that the domain wall DWa can move beyond a portion (a positionwith the dimension D2) having a maximum value VL2 of the volume (amaximum cross-section AL2) in the projection portion 512. The pulse P2has a pulse width t_(p2). Thereby, a current corresponding to thecurrent value ib flows in the magnetic member 50 during a periodcorresponding to the pulse width t_(p2).

As described with reference to FIG. 15, at the time of the start of thesupply of the pulse P2, the domain wall DW exists in the region near theconcave portion 521<k> or the region near the concave portion 522<k>.

When the domain wall DW exists in the concave portion 521<k>, the domainwall DWa in the concave portion 521<k> moves beyond the projectionportion 512<k> into the concave portion 522<k> by the energy due to thepulse P2 with the current value ib.

The current value ib of the pulse P2 is set to such a current value(e.g. a value less than the current value ia) that the domain wall DWbdoes not move beyond a portion (a position with the dimension D1) havinga maximum value VL1 of the volume (a maximum cross-section AL1) in theprojection portion 511. The energy (e.g. spin torque), which the domainwall in the concave portion 521<k> receives from the pulse P2, is theenergy by which the domain wall DWb can move into the projection portion512<k>, but is less than the energy by which the domain wall DWb canmove into the concave portion 521<k+1> via the projection portion511<k+1>.

Therefore, even if the energy due to the pulse P2 is applied to a domainwall which may exist in the concave portion 521<k>, the domain wall DWbcan move beyond the projection portion 512<k> but cannot move beyond theprojection portion 511<k+1>.

When a domain wall exists in the concave portion 522<k>, the domain wallDWb in the concave portion 522<k> receives the pulse P2 of the currentvalue ib. The current value ib of the pulse P2 is set to such a currentvalue (e.g. a value less than the current value ia) that the domain wallDWb does not move beyond a portion (a position with the dimension D1) C3having the maximum value VL1 of the volume in the projection portion511. The energy (e.g. spin torque), which the domain wall DWb in theconcave portion 522<k> receives from the pulse P2, is less than theenergy with which the domain wall DWb moves into the concave portion521<k+1> via the projection portion 511<k+1>.

Therefore, even if the energy due to the pulse P2 is applied to thedomain wall DWb which may exist in the concave portion 522<k>, thedomain wall DWb does not move beyond the projection portion 511<k+1>.

Accordingly, a domain wall DWz at the time when the pulse P2 is suppliedis located in the region between the position (the portion with thedimension D2) C2 having the maximum value of the volume (the maximumcross-section) of the projection portion 512<k> and the position (theportion with the dimension D1) C3 having the maximum value of the volume(the maximum cross-section) of the projection portion 511<k+1>.

After the stop of supply of the pulse P2, the magnetic state of themagnetic member 50 enters an equilibrium state (relaxation state).

In a relaxation period t_(rx2) after the supply of the pulse P2, thedomain wall DW moves, for example, by an internal magnetic fieldoccurring in the magnetic member of the constriction structure, to aportion (a portion with a smaller dimension) having a smaller volumethan the volume of the portion where the domain wall is currentlydisposed in the magnetic member 50, in such a manner that the domainwall DW enters a stabler energy state.

Therefore, as illustrated in FIG. 17, the domain wall, which may existbetween the concave portion 522<k> and the projection portion 512<k>,stabilizes in the concave portion 522<k>.

The domain wall, which may exist between the concave portion 522<k> andthe projection portion 511<k+1>, moves to the concave portion 522<k>.During the relaxation period t_(rx2) after the supply of the pulse P2,the domain wall, which may exist between the concave portion 522<k> andthe projection portion 511<k+1>, shifts to the concave portion 522<k>side.

In this manner, the domain wall, which is shifted by the shift currentSP (pulse P2) from the concave portion 522<k> of a certain memory cellMC<k> to the projection portion 511<k+1> side of a neighboring memorycell MC<k+1>, moves back into the concave portion 522<k>.

For the stabilization of energy, the domain wall in the projectionportion 512<k> shifts to the concave portion 522<k> side having asmaller volume (a smaller cross-section area).

As a result, during the relaxation period t_(rx2), an existenceprobability distribution Q4 of the domain wall DW exhibits a highexistence probability in the concave portion (the domain wall retentionportion) 522<k> between the memory cell MC<k> and the memory cellMC<k+1>.

In this manner, the domain wall memory 1 of the present embodimentexecutes the shift operation by supplying the shift current SP includingpulses P1 and P2 with different current values to the magnetic memberincluding projection portions with different dimensions.

In a certain domain wall memory, a shift pulse including one pulse issupplied to a memory cell in which one projection portion is provided,and the domain wall is moved to a target position by one-time shift.

Compared to a domain wall shift method of a certain domain wall memory,the domain wall memory 1 of the present embodiment can increase theexistence probability of the domain wall in the concave portion 522functioning as the domain wall retention portion of the memory cell MC.

As described above, the standard deviation σ of the existenceprobability distribution of the domain wall and the motion distance Lvary such that the relation of σ²/L is kept substantially constant.Compared to the method of moving the domain wall by one-time shift as ina certain domain wall memory, in the domain wall memory of the presentembodiment, the position of the domain wall is stabilized in a firstconcave portion by first-time domain wall shift (the variance of thedomain wall position is decreased), and then the domain wall is shiftedto the target position by second-time domain wall shift. Thereby, themotion distance of the domain wall by each one-time domain wall shiftbecomes shorter. Thus, in the present embodiment, the variance of theexistence probability distribution of the domain wall decreases.Therefore, in the domain wall memory of the present embodiment, thevariance of the position of the domain wall in the magnetic member (andin the memory cell) can be decreased.

As a result, the domain wall memory of the present embodiment cansuppress the occurrence of a shift error of the domain wall.

(c-4) Operation Sequence

Referring to FIG. 18 and FIG. 19, an operation sequence including ashift operation of the domain wall memory of the present embodiment willbe described. The shift operation using the shift pulse of the domainwall memory of the present embodiment is applicable to an operationsequence including a read operation, and to an operation sequenceincluding a write operation.

[Read Sequence]

FIG. 18 is a timing chart illustrating an example of an operationsequence including a shift operation and a read operation in the domainwall memory of the present embodiment.

The abscissa axis of FIG. 18 corresponds to time (time instant), and theordinate axis of FIG. 18 corresponds to the current value of current(I_(BL-WL)) flowing between the bit line and word line. In FIG. 18, thecurrent value is indicated by an absolute value. It should be noted thatthe polarity of the current I_(BL-WL) in a case where the currentI_(BL-WL) flows from the bit line to the word line is different from thepolarity of the current I_(BL-WL) in a case where the current I_(BL-WL)flows from the word line to the bit line.

<Time Instant T0 a>

The external device (e.g. a host device or a controller) 2 sends acommand and an address (hereinafter referred to as “selection address”)of a target of an operation to the domain wall memory 1 of the presentembodiment. At a time when a read operation is instructed, the externaldevice sends a read command to the domain wall memory 1.

The domain wall memory 1 receives the read command and the selectionaddress.

At time instant T0 a, based on the read command, the domain wall memory1 starts a read operation of data in a memory cell unit (hereinafterreferred to as “selected memory cell unit”) corresponding to theselection address. For example, by the read command, the data in memorycells MC in the selected memory cell unit are successively read.

<Time Instants T1 a and T2 a>

As illustrated in FIG. 18, at time instant Tia, switching current (alsoreferred to as “switching pulse” or “spike current”) Pa is supplied tothe selected memory cell unit as a current |I_(BL-WL)| flowing between aselected bit line and a selected word line in accordance with theselection address. In the memory cell unit to which the switchingcurrent Pa is supplied, the switching element 20 is turned on. Theselected memory cell unit is electrically connected to the bit line BLvia the switching element 20 which is in the ON state.

Thereby, the selected memory cell unit MU is set in an active state(selected state).

For example, the switching current Pa has a current value ia. However,the current value of the switching current Pa may be a value differentfrom the current value ia. When the current value of the switchingcurrent Pa is set to be equal to the current value of the shift pulseSP, the circuit configuration of the domain wall memory can besimplified.

A pulse width t_(sp) of the switching pulse Pa is less than the pulsewidth t_(p1), t_(p2) of the pulse P1, P2 of the shift current SP.Therefore, even if the switching current Pa flows into the magneticmember 50, there occurs no substantial motion of the domain wall due tothe switching current Pa.

After the supply of the switching current Pa (e.g. at time instant T2a), a hold current IHD is supplied to the selected memory cell unit asthe current |I_(BL-WL)|. The hold current IHD has a current value i1which can keep the ON state of the switching element 20. The currentvalue i1 is lower than the current value ia of the switching current Paand the domain wall shift threshold ith.

Thereby, the selected memory cell unit is set in a conductive state tothe selected bit line BL via the switching element 20 which is in the ONstate.

<Time Instants T3 a and T4 a>

After the selected memory cell unit is set in the active state, thesupply of the shift current SP (the shift operation) in a first cycle isstarted. The shift circuit 160 supplies the shift current SP to theselected memory cell unit.

For example, by the shift operation of the read sequence, the magneticdomain (magnetization) is shifted by one bit from a memory cell on thelower end side (word line side) of the selected memory cell unit MU to amemory cell MC on the upper end side (bit line side) of the selectedmemory cell unit.

At time instant T3 a, the first pulse (main pulse) P1 of the shiftcurrent SP is supplied to the magnetic member 50 by the shift circuit160. The pulse P1 has a current value ia. The first pulse P1 has a pulsewidth t_(p1). Note that the pulse width t_(p1) is a full width at halfmaximum of the pulse P1.

The current pulse P1 with the current value ia flows in the magneticmember 50 during a period corresponding to the pulse width t_(p1).Thereby, all domain walls in the magnetic member 50 move. For example,the domain wall DW shifts from the concave portion 522<k−1> of a certainmemory cell MC<k−1> in the magnetic member 50 into an immediatelyadjacent memory cell MC<k> (see, e.g. FIG. 13 and FIG. 14).

For example, the pulse P1 is supplied to the magnetic member 50 of thememory cell unit MU such that the pulse P1 flows from the bit line BLside toward the word line WL side. The domain wall moves in a directionof the motion of electrons due to the supply of the pulse P1.

In the present embodiment, the domain wall moves from the word line WLside toward the bit line BL side in the direction of motion ofelectrons. In this case, one or more domain walls in the magnetic member50 shift substantially simultaneously from the word line WL side towardthe bit line BL side.

By the supply of the pulse P1, the domain wall DW is disposed in theconcave portion 521<k> and concave portion 522<k> in the memory cellMC<k> at the destination of motion. In the concave portion 521<k> andconcave portion 522<k>, the domain wall DW may exist in the magneticmember 50 with the distribution Q1 of the existence probabilityillustrated in FIG. 14.

After the passage of the period corresponding to the pulse width t_(p1)from the start of supply of the pulse P1 (for example, at time instantT4 a), the shift circuit 160 lowers the current value of the suppliedcurrent |I_(BL-WL)| from the current value is to the current value i1.

Thereby, the supply of the pulse P1 is stopped. By the supply of thecurrent IHD with the current value i1, the switching element 20 keepsthe ON state.

During the relaxation period t_(rx1) after the stop of supply of thepulse P1, the domain wall of a certain memory cell MC<k> may exist inthe magnetic member 50 with the existence probability Q2 a, Q2 billustrated in FIG. 15, by the relaxation of the domain wall by theconstriction structure (projection portion 511, 512 and concave portion521, 522) of the magnetic member 50.

Note that, in the present embodiment, the hold current IHD flows in themagnetic member 50 during the relaxation period t_(rx1), t_(rx2).

By the supply of the hold current IHD, a stray magnetic field due to thehold current IHD, or a weak domain wall driving force due to the holdcurrent IHD, occurs in the magnetic member 50. The stray magnetic fielddue to the hold current IHD is added to an effective magnetic field dueto the constriction region (concave portion). Thereby, the relaxationperiod t_(rx1), t_(rx2) is shortened. As a result, the speed of thememory operation in the domain wall memory can be increased.

<Time Instants T5 a and T6 a>

At time instant T5 a after the passage of the relaxation period t_(rx1)from the stop of supply of the pulse P1, the second pulse P2 of theshift current SP is supplied from the selected bit line BL to themagnetic member 50 by the shift circuit 160. The pulse P2 has a currentvalue ib which is less than the current value ia. The pulse P2 has apulse width t_(p2). Note that the pulse width t_(p2) is a full width athalf maximum of the pulse P2.

By the supply of the pulse P2, the domain wall DW shifts into a regionnear the concave portion 522<k> of a certain memory cell MC<k> (see,e.g. FIG. 16).

Thereby, the domain wall DW may exist in a region between the apexportion of the projection portion 512 of a certain memory cell MC<k> andthe apex portion of the projection portion 511<k+1> of the memory cellMC<k+1> in a manner to have the existence probability distribution Q3 a,Q3 b illustrated in FIG. 16.

After the passage of the period corresponding to the pulse width t_(p2)from the start of supply of the pulse P2 (for example, at time instantT6 a), the shift circuit 160 lowers the current value of the suppliedcurrent |I_(BL-WL)| from the current value ib to the current value i1.

Thereby, the supply of the pulse P2 is stopped. By the hold current IHD,the switching element 20 keeps the ON state.

The magnetic domain (magnetization), which is shifted into the read cellMCA (cell region 510A) in the shift operation, affects the magnetizationof the storage layer 11 of the MTJ element 10 via the magnetic layer 59.The direction of magnetization of the storage layer 11 is set to agreewith the direction of magnetization in the read cell MCA.

In this manner, the shift operation of the first cycle in the readsequence is completed.

For example, a certain period (relaxation period) t rx2 passes from thestop of supply of the pulse P2. In the relaxation period t_(rx2), theexistence probability of the position of the domain wall DW stabilizesin the concave portion 522 of the memory cell which retains the domainwall DW, as indicated by the distribution Q4 in FIG. 17.

In this manner, in the present embodiment, the variance of the positionof the domain wall after the supply of the shift current is suppressed.

<Time Instants T7 a and T8 a>

In the first read cycle, after the shift operation, the read circuit 150executes a read operation.

At time instant T7 a after the passage of the relaxation period t_(rx2),the read circuit 150 supplies a read current (read pulse) PRD to theselected memory cell unit MU.

A current value i2 of the read current PRD is less than a magnetizationreversal threshold of the storage layer 11 and the domain wall shiftthreshold ith of the magnetic member 50. The current value i2 is greaterthan the current value i1. For example, the read current PRD flows in adirection from the word line WL toward the bit line BL.

The current value of the current flowing in the bit line BL and thepotential of the bit line BL vary in accordance with the magnetizationalignment state of the reference layer 12 and storage layer 11 in theMTJ element 10.

The read circuit 150 senses the current value of the current flowing inthe bit line BL, or the potential of the bit line BL.

Based on the sensed result, the read circuit 150 determines the data inthe read cell MCA.

Thereby, in the first read cycle, data is read.

At time instant T8 a, the read circuit 150 lowers the current value ofthe supplied current |I_(BL-WL)| from the current value i2 to thecurrent value i1.

Thus, the first read cycle is completed.

Following the first read cycle, a second read cycle is executed.

Like the first read cycle, a shift operation in the second read cycle isexecuted. By the motion of the domain wall by the shift operation, thedata is shifted into the read cell MCA.

When the domain wall DW is moved by the shift operation using the shiftcurrent SP in the present embodiment, the variance of the position ofthe domain wall DW in the concave portion 522 is small. Therefore, inthe shift operation of the second read cycle, the variance of theposition of the shifted domain wall DW becomes small. As a result, inthe domain wall memory of the present embodiment, the shift error in theread sequence is reduced.

After the shift operation, a read operation in the second read cycle isexecuted on the read cell MCA which stores the shifted data.

In this manner, in the read sequence, the shift operation and the readoperation are repeatedly executed.

<Time Instant T9 a>

After a predetermined number of read cycles are executed, the readcircuit 150 stops, at time instant T9 a, the supply of the current|I_(BL-WL)| to the selected memory cell unit. The current value of thecurrent |I_(BL-WL)| is set to zero. Thereby, the switching element 20 isset in the OFF state.

As a result, the selected memory cell unit is set in an inactive state(non-selected state, OFF state).

The read data is sent from the read circuit 150 to the I/O circuit 170at a predetermined timing. Thereby, the data is transferred from thedomain wall memory 1 to the external device 2.

As described above, in the domain wall memory of the present embodiment,the read sequence is completed.

[Write Sequence]

FIG. 19 is a timing chart illustrating an example of an operationsequence (write sequence) including a shift operation and a writeoperation in the domain wall memory of the present embodiment.

The abscissa axis of FIG. 19 corresponds to time (time instant), and theordinate axis of FIG. 19 corresponds to the current value (absolutevalue) of current (|I_(BL-WL)|) flowing between the bit line and wordline. In FIG. 19, a current (write current PWR) flowing in the writeline is illustrated. The write current PWR has a positive polarity(positive current value) or a negative polarity (negative current value)in accordance with the direction of flow in the write line FL.

<Time Instants T0 b, T1 b, and T2 b>

The external device 2 sends a write command, an address of a target ofdata write, and data (write data) to be written in the memory cell array100, to the domain wall memory 1 of the present embodiment.

The domain wall memory 1 receives the write command, the selectionaddress and the write data, for example, at time instant T0 b.

Based on the write command, the domain wall memory 1 starts a data writesequence in a memory cell unit (selected memory cell unit) correspondingto the selection address. The write data is transferred from the I/Ocircuit 170 to the write circuit 140.

For example, by the write command, data is successively written inmemory cells in the selected memory cell unit.

As illustrated in FIG. 19, substantially similarly as in the readsequence, at time instant T1 b, a switching current Pa is supplied tothe selected bit line BL. Thereby, the selected memory cell unit MU iselectrically connected to the bit line BL via the switching element 20which is in the ON state.

After the supply of the switching current Pa (e.g. at time instant T2b), the current value of the current supplied to the selected memorycell unit MU is set to the current value i1 of the hold current IHD ofthe switching element 20.

<Time Instants T3 b and T4 b>

After the selected memory cell unit MU is set in the active state, ashift operation of a first cycle in the write sequence is started. Theshift circuit 160 supplies the shift current SP to the selected memorycell unit MU.

The shift current SP of the shift operation in the write sequence issubstantially the same as the shift current SP of the shift operation inthe read sequence. However, in the write operation of the domain wallmemory of the LIFO method, the shift current SP is supplied to theselected memory cell unit MU, for example, such that the shift currentSP flows from the word line WL to the bit line BL. In this case,electrons due to the shift current SP move from the bit line BL towardthe word line WL. In the present embodiment, the domain wall moves fromthe bit line BL side toward the word line WL side in the direction ofmotion of electrons.

At time instant T3 b, the pulse P1 of the shift current SP is suppliedto the selected memory cell unit. The pulse P1 has a current value ia.The pulse P1 has a pulse width t_(p1).

The pulse P1 is supplied to the magnetic member 50 during a periodcorresponding to the pulse width t_(p1). Thereby, all domain walls inthe magnetic member 50 move.

For example, by the shift operation of the write sequence, the magneticdomain (magnetization) is shifted by one bit from a memory cell (e.g. awrite cell MCA) on the upper end side (bit line side) of the selectedmemory cell unit MU to a memory cell MC on the lower end side (word lineside) of the selected memory cell unit MU.

By the supply of the pulse P1, the domain wall moves into the projectionportion 512 (a region between the concave portion 521 and the concaveportion 522). The existence probability of the position of the domainwall in this region is as indicated by the state Q1 illustrated in FIG.14.

For example, at time instant T4 b, the shift circuit 160 stops thesupply of the pulse P1. The shift circuit 160 lowers the current valueof the current |I_(BL-WL)| from the current value ia to the currentvalue i1.

During the relaxation period t_(n)ci, the domain wall may exist in theconcave portion 521 or concave portion 522, for example, withdistribution Q2 a, Q2 b illustrated in FIG. 15.

<Time Instants T5 b and T6 b>

At time instant T5 b after the passage of the relaxation period t_(rx1)from the stop of supply of the pulse t_(rx1) P1, the pulse P2 of theshift current SP is supplied to the selected memory cell unit MU. Thepulse P2 has a current value ib which is less than the current value ia.The pulse P2 has a pulse width t_(p2).

By the supply of the pulse P2, the domain wall DW may exist in a regionbetween the apex portion of the projection portion 512 of a certainmemory cell MC<k> and the apex portion of the projection portion511<k+1> of the memory cell MC<k+1> in a manner to have the existenceprobability distribution Q3 a, Q3 b illustrated in FIG. 16.

At time instant T6 b, the shift circuit 160 stops the supply of thepulse P2. The shift circuit 160 lowers the current value of the current|I_(BL-WL)| from the current value ib to the current value i1.

As indicated by the distribution Q4 in FIG. 17, during a certain period(relaxation period) t_(rx2) from the stop of supply of the pulse P2, theposition of the domain wall DW stabilizes in the concave portion 522 ofa certain memory cell MC<k> (or near the concave portion 522).

Thereby, in the present embodiment, the variance of the position of thedomain wall after the supply of the shift current SP is suppressed.

In this manner, the shift operation in the first write cycle of thewrite sequence is completed.

<Time Instants T7 b and T8 b>

In the write sequence, after the shift operation, a write operation isexecuted on the selected memory cell unit MU.

For example, at time instant T7 b, the write circuit 140 supplies awrite current PWR to the write line FL. The write current PWR flows inthe write line FL. Thereby, a magnetic field is generated around thewrite line FL. The direction of the magnetic field varies depending onthe direction of flow of the write current PWR.

The direction of flow of the write current PWR is set in accordance withwrite data (“1” data or “0” data). For example, when the write currentPWR with a first polarity (e.g. write current with a positive currentvalue) is supplied to the write line FL, “1” data is written in thewrite cell MCA. For example, when the write current PWR with a secondpolarity that is different from the first polarity (e.g. write currentwith a negative current value) is supplied to the write line FL, “0”data is written in the write cell MCA.

The magnetic field from the write line FL is applied to the magneticlayer 59. The direction of magnetization of the magnetic layer 59 is setto a direction corresponding to the direction of the magnetic field.

The magnetization of the magnetic layer 59 affects the magnetization(magnetic domain) of the write cell MCA (cell region 510A). Thedirection of magnetization of the write cell MCA is set to agree withthe direction of magnetization in the magnetic layer 59. Thereby, thewrite data is written in the write cell MCA in the selected memory cellunit MU.

Thus, the write operation in the first write cycle of the write sequenceis completed.

Following the first write cycle, a second write cycle is executed. Likethe first write cycle, a shift operation in the second write cycle isexecuted. By the shift operation, the data in the write cell MCA isshifted to an immediately neighboring memory cell.

When the domain wall DW is moved, in the first write cycle, by the shiftoperation using the shift current in the present embodiment, thevariance of the position of the domain wall DW in the concave portion522 of the memory cell that retains the domain wall is small. Therefore,in the shift operation in the second write cycle, the variance of theposition of the shifted domain wall DW becomes small.

As a result, in the domain wall memory of the present embodiment, theshift error in the write sequence is reduced.

In this manner, in the write sequence, the shift operation and the writeoperation are repeatedly executed.

<Time Instant T9 b>

After a predetermined number of write cycles are executed, at timeinstant T9 b, the current value of the current |I_(BL-WL)| is set tozero. Thereby, the switching element 20 is set in the OFF state.

As a result, the selected memory cell unit is set in an inactive state(non-selected state, OFF state).

In this manner, the write data from the external device 2 is written inthe selected memory cell unit in the memory cell array 100.

As described above, in the magnetic memory of the present embodiment,the write sequence is completed.

(e) Conclusion

In the shift operation of the domain wall memory, the domain wall in themagnetic member moves in the magnetic member by the shift pulse.

When the domain wall moves in the magnetic member having theconstriction structure, since the domain wall has a certain width, thevolume change rate of the domain wall becomes small in a portion with amaximum value of the volume in the magnetic member of the constrictionstructure and/or in a portion with a minimum value of the volume (and inregions near these portions).

Thus, at the time of the shift operation of the domain wall shiftmemory, there is a possibility that the domain wall does not exist in atarget position.

As the motion distance of the domain wall by a certain pulse becomeslonger, the error between the target position of the domain wall and theposition of the actually shifted domain wall tends to increase.

As a result, there is a possibility that the shift error of the domainwall (magnetic domain) increases in the domain wall memory.

In the domain wall memory of the present embodiment, the magnetic memberof the constriction structure includes the first projection portion andsecond projection portion which neighbor each other in the direction ofmotion of the domain wall. The first projection portion has a firstdimension in the first direction crossing the direction of motion of thedomain wall. The second projection portion has a second dimension in thefirst direction. The first dimension is greater than the seconddimension. The volume of the first projection portion is greater thanthe volume of the second projection portion. In the magnetic member ofthe constriction structure, the first concave portion is providedbetween the first projection portion and the second projection portion.The second projection portion is provided between the first concaveportion and the domain wall retention portion (second concave portion)of the memory cell.

In the present embodiment, at the time of the shift operation of thedomain wall memory, the shift pulse including the first pulse and thesecond pulse is supplied to the magnetic member. The current value ofthe second pulse is less than the current value of the first pulse. Atthe time of the shift operation of the domain wall memory of the presentembodiment, the second pulse is supplied to the magnetic member afterthe first pulse is supplied to the magnetic member.

By the supply of the first pulse, the domain wall is shifted into theregion (concave portion) between the first projection portion and secondprojection portion, or into the domain wall retention portion of thememory cell.

By the supply of the second pulse, the domain wall in the first concaveportion shifts from the concave portion to the domain wall retentionportion via the second projection portion. In addition, even if thesecond pulse is supplied, the domain wall in the domain wall retentionportion can exist in a region near the domain wall retention portion.

In the domain wall memory of the present embodiment, by the two-timepulse supplies, the domain wall is moved in two steps, and the domainwall is shifted to the target position. Therefore, in the domain wallmemory of the present embodiment, the motion distance of the domain wallby one-time pulse supply becomes short. Thereby, in the domain wallmemory of the present embodiment, the motion of the domain wall over along distance can be suppressed.

In the present embodiment, during the relaxation period after the supplyof the second pulse, the position of the domain wall stabilizes in thedomain wall retention portion (or in the region near the domain wallretention portion) by the internal magnetic field of the magnetic memberdue to the constriction structure which the magnetic member has.

Thereby, the domain wall memory of the present embodiment can suppressthe variance of the position of the domain wall at the time of the shiftoperation.

Therefore, the domain wall memory of the present embodiment can suppressthe shift error of the domain wall.

Accordingly, the domain wall memory of this embodiment can enhance thereliability of the operation.

(2) Second Embodiment

Referring to FIG. 20, a magnetic memory of a second embodiment and acontrol method thereof will be described.

FIG. 20 is a waveform diagram illustrating a shift pulse used in theshift operation of the magnetic memory (e.g. domain wall memory) of thepresent embodiment. The abscissa axis of FIG. 20 corresponds to time,and the ordinate axis of FIG. 20 corresponds to a current value.

As illustrated in FIG. 20, a shift current SPa may have a pulse waveformwith two consecutive pulses P1 and P2. In the present embodiment, theshift current SPa has a stepwise pulse shape.

The shift current SPa has a current value ia in a period TA, and has acurrent value ib in a period TB which is continuous with the period TA.

The pulse P1 has the current value ia in the period TA from time instantta to time instant tb.

The pulse P2 has the current value ib in the period TB from time instanttb to time instant tc.

The magnetic memory of the present embodiment can obtain the sameadvantageous effects as in the first embodiment, by the shift operationusing the shift current SPa of FIG. 20.

When the shift current SPa illustrated in FIG. 20 is used in the shiftoperation of the domain wall memory, the relaxation period between twopulses P1 and P2 during the shift operation period can be eliminated.

As a result, the domain wall memory of the present embodiment canshorten the shift operation period.

Note that, in the present embodiment, the pulse waveform of the shiftcurrent SP may be a triangular wave. In this case, the current value ofthe shift current SP gradually decreases from the start of supply of thecurrent to the stop of supply of the current. For example, the shiftcurrent SP of the triangular wave has the current value is or more in acertain period from the start of supply of the shift current, and has avalue which is less than the current value is and is not less than thecurrent value ib in a period which is continuous with this period. Inaddition, the pulse shape of each pulse included in the shift currentmay be a triangular wave.

(3) Third Embodiment

Referring to FIG. 21 to FIG. 24, a magnetic memory of a third embodimentand a manufacturing method of the magnetic memory will be described.

FIG. 21 is a cross-sectional view illustrating a structure example ofthe magnetic memory of the present embodiment.

As illustrated in FIG. 21, in a magnetic member 50A of the memory cellunit, projection portions 511A and 512A and concave portions 521A and522A may have rectangular cross-sectional shapes.

Like the above-described embodiments, the magnetic member 50A has aconstriction structure. The dimension (diameter) of the magnetic member50A in the parallel direction to the upper surface of the substrate 9cyclically varies in the Z direction.

The magnetic member 50A is composed of a cylindrical magnetic layer.

The magnetic member 50A includes a plurality of projection portions 511Aand 512A and a plurality of concave portions 521A and 522A.

Each memory cell MC includes two projection portions 511A and 512A inthe cell region 510 thereof. The concave portion 521A is providedbetween the two projection portions 511A and 512A in the cell region510. The concave portion 522A is provided at one end and the other endof the memory cell MC (cell region 510).

In the present embodiment, each of the projection portions 511A and 512Aand concave portions 521A and 522A has a rectangular cross-sectionalshape. For example, each of the projection portions 511A and 512A andconcave portions 521A and 522A has a circular (or elliptic) planar shapeas viewed in the Z direction.

A dimension (maximum dimension) D1A of the projection portion 511A inthe parallel direction to the upper surface of the substrate 9 isgreater than a dimension (maximum dimension) D2A of the projectionportion 512A in the parallel direction to the upper surface of thesubstrate 9. The volume (volume of the magnetic portion) of theprojection portion 511A is greater than the volume (volume of themagnetic portion) of the projection portion 512A. The cross-sectionalarea of a portion with the dimension D1A in the projection portion 511Ais greater than the cross-sectional area of a portion with the dimensionD2A in the projection portion 512A.

A dimension D3A, D4A of the concave portion 521A, 522A in the paralleldirection to the upper surface of the substrate 9 is less than thedimension D1A and dimension D2A. The dimension D4A of the concaveportion 522A in the parallel direction to the upper surface of thesubstrate 9 is substantially equal to the dimension D3A of the concaveportion 521A in the parallel direction to the upper surface of thesubstrate 9. The volume of the concave portion 521A, 522A is less thanthe volume of the projection portion 512A.

At the time of the shift operation of the domain wall memory of thepresent embodiment, the shift current SP of FIG. 11 (or the shiftcurrent of FIG. 12, or the shift current SPa of FIG. 20) is supplied tothe memory cell unit (magnetic member) with the structure of FIG. 20.

Thereby, the domain wall memory of the present embodiment, whichincludes the magnetic member 50A of the constriction structure of FIG.21, can reduce the shift error.

Referring to FIG. 22 to FIG. 24, a manufacturing method of the domainwall memory of the present embodiment will be described.

FIG. 22 to FIG. 24 are cross-sectional process views for describing themanufacturing method of the domain wall memory of the presentembodiment.

As illustrated in FIG. 22, a plurality of layers 950, 951 and 952 areformed on the upper surface of the substrate 9, such that the layers arearranged at predetermined cycles in the Z direction. Thereby, a sackedbody 900A is formed on the substrate 9.

For example, a layer 950 is formed above the upper surface of thesubstrate 9. A layer 951 is formed on the layer 950. A layer 950 isformed on the layer 951. A layer 952 is formed above the layer 951 viathe layer 950.

In this manner, the layers 951 and layers 952 are alternately stackedabove the substrate 9 in the Z direction via the layers 950.

The materials of the layers 950, 951 and 952 are different from eachother. The combination of materials of the layers 950, 951 and 952 isselected such that an etching selectivity between the layers 950, 951and 952 can be secured by etching (wet etching) which will be describedlater.

The materials of the layers 950 and 951 are selected such that theetching amount of the layer 951 under a certain etching condition isgreater than the etching amount of the layer 950. The materials of thelayers 950, 951 and 952 are selected such that the etching amount of thelayer 952 under a certain etching condition is greater than the etchingamount of the layer 950 and is less than the etching amount of the layer951.

For example, the layer 950 is a silicon nitride layer (SiN layer). Thelayer 951 is a silicon oxide layer (SiO₂ layer). The layer 952 is asilicon oxynitride layer (SiON layer).

After the stacked body 900A is formed, a hole 990A is formed in thestacked body 900A by lithography and etching.

As illustrated in FIG. 23, etching (e.g. wet etching) is performed onthe SiO₂ layers 951 and SiON layers 952 via the hole 990A.

Surfaces of the layers 951 and 952 retreat in the parallel direction tothe upper surface of the substrate 9.

As a result, recesses 981 and 982 are formed in the stacked body 900A.The recesses 981 are formed at positions of the layers 951 in thestacked body 900A. The recesses 982 are formed at positions of thelayers 952 in the stacked body 900A.

The etching amounts of the layers 951 and 952 for a supplied etchant(e.g. hydrofluoric acid solution) are different. A depth G1A of therecess 981 in the SiO₂ layer 951 is greater than a depth G2A of therecess 982 in the SiON layer 952. The SiN layers 950, for instance, arehardly etched at the time of etching the SiO₂ layers 951 and SiON layers952.

Therefore, the dimensions of retreat (the depth of recesses) of thelayers in the parallel direction to the upper surface of the substrate 9vary depending on positions of the layers 950, 951 and 952.

As illustrated in FIG. 24, a magnetic layer 500A is formed on the layers950, 951 and 952 in the hole 990A. Thereby, the projection portions 511Aand 512A having rectangular cross-sectional shapes are formed at thepositions of the layers 951 and 952. The concave portions 521A and 522Ahaving rectangular cross-sectional shapes are formed at the positions ofthe layers 950.

The magnetic member 50A including the projection portions 511A and 512Ais formed in the hole 990A. The dimension in the Y direction (and Xdirection) in the formed magnetic member 50A cyclically varies in the Zdirection. In this manner, the magnetic member 50 having theconstriction structure is formed.

Thereafter, like the above-described example, the reproducing element,switching element and various interconnects of the memory cell unit areformed above the magnetic member 50.

Thereby, the domain wall memory of the present embodiment is completed.

As described above, the magnetic memory of the present embodiment canobtain the same advantageous effects as in the above-described otherembodiments.

(4) Fourth Embodiment

Referring to FIG. 25, a magnetic memory of a fourth embodiment will bedescribed.

FIG. 25 is a cross-sectional view illustrating a configuration exampleof the magnetic memory of the present embodiment.

As illustrated in FIG. 25, in a magnetic member 50B with a constrictionstructure, projection portions 511B, 512B and concave portions 521B,522B may have curved surfaces.

Like the above-described embodiments, the magnetic member SOB has theconstriction structure. The dimension (diameter) of the magnetic member50B in the parallel direction to the upper surface of the substrate 9cyclically varies in the Z direction.

The magnetic member 50B is composed of a cylindrical magnetic layer.

The magnetic member 50B includes projection portions 511B and 512B andconcave portions 521B and 522B.

Each memory cell MC includes two projection portions 511B and 512B in acell region 510 thereof. The concave portion 521B is provided betweenthe two projection portions 511B and 512B in the cell region 510. Theconcave portion 522B is provided at an end portion of the memory cell MC(cell region 510).

In the present embodiment, each of the projection portions 511B and 512Band concave portions 521B and 522B has an elliptic (or circular)cross-sectional shape as viewed in the X direction (or Y direction). Forexample, each of the projection portions 511B and 512B and concaveportions 521B and 522B has an elliptic (or circular) plan-view shape asviewed in the Z direction.

A dimension (maximum dimension) D1B of the projection portion 511E inthe parallel direction to the upper surface of the substrate 9 isgreater than a dimension (maximum dimension) D2B of the projectionportion 512B in the parallel direction to the upper surface of thesubstrate 9. The volume (volume of the magnetic portion) of theprojection portion 511B is greater than the volume (volume of themagnetic portion) of the projection portion 512B.

A dimension D3B and D4B of the concave portion 521B and 522B in theparallel direction to the upper surface of the substrate 9 is less thanthe dimension DIB and dimension D2B. The volume of the concave portion521B and 522B is less than the volume of the projection portion 512B.

At the time of the shift operation of the domain wall memory of thepresent embodiment, the shift current SP of FIG. 11 (or the shiftcurrent of FIG. 12, or the shift current SPa of FIG. 20) is supplied tothe memory cell unit (magnetic member) with the structure of FIG. 20.

Thereby, the domain wall memory of the present embodiment can reduce theshift error.

Accordingly, the magnetic memory of the present embodiment can obtainthe same advantageous effects as in the above-described otherembodiments.

(5) Fifth Embodiment

Referring to FIG. 26, a magnetic memory of a fifth embodiment and acontrol method thereof will be described.

FIG. 26 is a schematic view illustrating a configuration example of themagnetic memory (e.g. a domain wall memory) of the present embodiment.

As illustrated in FIG. 26, a magnetic member 50C having a constrictionstructure may be a plate-shaped layer extending in the paralleldirection to the upper surface of the substrate 9.

In the present embodiment, the magnetic member 50C extends, for example,in the X direction. The magnetic member 50C includes projection portions511C and 512C and concave portions 521C and 522C (522Ca and 522Cb). Inthe magnetic member 50C, the projection portions 511C and projectionportions 512C are alternately arranged in the X direction.

Each of the projections 511C and 512C includes a portion projecting inthe Y direction. For example, each of the projections 511C and 512C hasa hexagonal plan-view shape as viewed in the Z direction. Note that theprojection 511C and 512C may have an octagonal plan-view shape as viewedin the Z direction.

The projection portion 511C is provided between the concave portion 521Cand concave portion 522Ca. The projection portion 512C is providedbetween the concave portion 521C and concave portion 522Cb. The concaveportion 521C is provided between the projection portion 511C andprojection portion 512C.

For example, the projection portions 511C and 512C have certaindimensions L1C and L2C, respectively, in the X direction. For example,the concave portions 521C and 522C have dimensions L3C and L4C,respectively, in the X direction.

Each memory cell MC includes the projection portion 511C and 512C andthe concave portion 521C and 522C in the cell region 510 thereof. Eachconcave portion 522C is shared by two memory cells MC neighboring in theX direction.

A domain wall is retained in the concave portion 522 of the memory cellMC (cell region 510).

A dimension (e.g. a maximum dimension) D1C of the projection portion511C in the Y direction is greater than a dimension (e.g. a maximumdimension) D2C of the projection portion 512C in the Y direction. Thevolume of the projection portion 511C is greater than the volume of theprojection portion 512C.

A dimension D3C of the concave portion 521C in the Y direction is lessthan the dimension D1C and D2C. A dimension D4C of the concave portion522C in the Y direction may be substantially equal to, or may bedifferent from, the dimension D3C.

In this manner, in the present embodiment, the dimension of theplate-shaped magnetic member 50C cyclically varies in the extendingdirection of the magnetic member.

At the time of the shift operation of the domain wall memory of thepresent embodiment, the shift current SP of FIG. 11 (or the shiftcurrent SP of FIG. 12, or the shift current SPa of FIG. 20) is suppliedto the memory cell unit (magnetic member) with the structure of FIG. 26.

Thereby, the domain wall memory of the present embodiment can reduce theshift error.

As a result, the magnetic memory of the present embodiment can obtainthe same advantageous effects as in the above-described embodiments.

(6) Modifications

Referring to FIG. 27 to FIG. 29, modifications of the magnetic memoriesof the embodiments will be described.

FIG. 27 is a schematic view illustrating a modification of the magneticmemories of the embodiments.

As illustrated in FIG. 27, in the memory cell array, the write line FLfor data write may be provided on the word line side.

For example, in the memory cell array including the magnetic member 50extending in the Z direction, the write line FL is provided on the lowerend side of the magnetic member 50.

A memory cell MCB, which is closest to the word line side of themagnetic member 50, is used as a write cell. In this case, the memorycell MCA, which is closest to the bit line side of the magnetic member,is used only as a read cell, without being used as a write cell.

For example, the write line FL neighbors the write cell on the lower endside of the magnetic member 50 in the Y direction.

A magnetic field due to the write current PWR supplied to the write lineFL is applied to the write cell MCB. The direction of magnetization inthe write cell MCB is set in accordance with the direction of themagnetic field. Thereby, data is written in the write cell MCB.

At the time of data write and at the time of data read, the data in thememory cell MC, MCA, and MCB is shifted from the word line side towardthe bit line side.

For example, the domain wall memory including the memory cell unit ofFIG. 27 functions as a domain wall shift memory (e.g. shift register) ofa FIFO (First-in First-out) method.

FIG. 28 is a schematic diagram illustrating a modification of the domainwall memories of the embodiments. In the domain wall memory of FIG. 28,data is written in the magnetic member 50 by an STT method.

The MTJ element 10 on the magnetic layer 59 is used as a reproducingelement and is used as a recording element (write element).

In this case, a write line for a magnetic field write method is notprovided in the memory cell array 100.

At the time of the write operation, a write current (write pulse) PWRxis supplied to the MTJ element 10. In accordance with data to be writtenin the write cell, the write current PWRx flows in a direction from thebit line BL to the word line WL, or flows in a direction from the wordline WL to the bit line EL.

The direction of magnetization in the storage layer 11 and magneticlayer 59 is controlled by spin torque due to the write current PWRxflowing in the MTJ element 10. The magnetization direction of the writecell MCA is set in accordance with the magnetization direction of themagnetic layer 59.

Thereby, the magnetization direction of the write cell MCA is controlledin accordance with the write data.

In this manner, by the STT method, write data is written in the memorycell unit MC.

The current value of the write current PWRx is greater than the currentvalue of the read current PRD. In order to prevent an unintended shiftoperation by the write current PWRx and an unintended write operation bythe shift current SP, the pulse shape (at least one of the current valueand the pulse width) of the write current PWRx is set as appropriate.

For example, the domain wall memory of FIG. 28 functions as a domainwall shift memory (shift register) of the LIFO method.

FIG. 29 is a schematic view illustrating a modification of the memorycell array of the domain wall memories of the embodiments.

As illustrated in FIG. 29, an MTJ element 10W for the write by the STTmethod may be provided on the lower end side (word line side) of themagnetic member 50.

The MTJ element 10W is provided between the magnetic member 50 and theword line WL.

The MTJ element 10W includes a storage layer 11W, a reference layer 12Wand a nonmagnetic layer (tunnel barrier layer) 13W. The storage layer11W is provided between the word line WL and a lower end (bottomportion) of the magnetic member 50. The reference layer 12W is providedbetween the storage layer 11W and the word line WL. The tunnel barrierlayer 13W is provided between the storage layer 11W and the referencelayer 12W.

For example, the storage layer 11W is in direct contact with themagnetic member 50. However, a magnetic layer may be provided betweenthe storage layer 11W and the magnetic member 50. When a magnetic layer(not shown) is provided between the storage layer 11W and the magneticmember 50, the magnetic layer is put in direct contact with the storagelayer 11W and the magnetic member 50.

A memory cell MCB, which is closest to the word line side of themagnetic member 50, is used as a write cell. In this case, the memorycell MCA, which is closest to the bit line side of the magnetic member,is used only as a read cell.

At the time of the write operation, a write current PWRx flows betweenthe MTJ element 10W and the magnetic member 50. The direction of flow ofthe write current PWRx is set in accordance with the data to be writtenin the write cell MCB. The direction of magnetization in the storagelayer 11W is controlled by spin torque due to the write current PWRx.The magnetization direction of the write cell MCB is set in accordancewith the magnetization direction of the storage layer 11W.

In order to secure the reliability of the operation, the characteristics(e.g. a magnetization switching threshold value of the storage layer) ofthe MTJ element 10W functioning as the recording element may bedifferent from the characteristics of the MTJ element 10 functioning asthe reproducing element.

For example, the domain wall memory of FIG. 29 functions as a domainwall shift memory (shift register) of the FIFO method.

Note that in the domain wall memories of the modifications of FIG. 27,FIG. 28 and FIG. 29, the magnetic member 50 may be a plate-shapedmagnetic layer.

In the shift operations of the domain wall memories of thesemodifications, the above-described shift pulse (shift current) includingpulses is used.

Thereby, the domain wall memories of these modifications can obtainsubstantially the same advantageous effects as in the above-describedembodiments.

(7) Others

In the above embodiments, the magnetic memory (e.g. domain wall memory,and domain wall shift memory) is illustrated as the device utilizing theshift operation of the domain wall in the magnetic member. However, thedevice of each embodiment is not limited to the magnetic memory, if thedevice can use, in the shift operation of the domain wall in themagnetic member, the shift pulse (shift current) including the pulsesdescribed in each embodiment.

The control method of the device of each embodiment is not limited tothe shift operation of the domain wall in the magnetic memory. Thecontrol method of the device of each embodiment is also applicable tocontrol methods (operations) of devices other than the magnetic memory,if such devices utilize the shift operation of the domain wall in themagnetic member.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A magnetic memory comprising: a magnetic memberincluding a first portion with a first dimension in a first direction, asecond portion spaced from the first portion in a second directioncrossing the first direction and having a second dimension in the firstdirection, a third portion provided between the first portion and thesecond portion and having a third dimension in the first direction, anda fourth portion provided between the first portion and the thirdportion and having a fourth dimension in the first direction; and acircuit configured to supply a shift pulse including a first pulse and asecond pulse to the magnetic member, and to move a domain wall in themagnetic member in the second direction, wherein the third dimension isless than the first dimension, and the second dimension and the fourthdimension is less than the third dimension, and the first pulse has afirst current value, and the second pulse has a second current valuewhich is less than the first current value.
 2. The magnetic memory ofclaim 1, wherein the second pulse is supplied to the magnetic memberafter the first pulse is supplied to the magnetic member.
 3. Themagnetic memory of claim 1, wherein the first pulse moves the domainwall from the first portion toward the second portion, and the secondpulse moves the domain wall in the fourth portion into the secondportion.
 4. The magnetic memory of claim 1, wherein the shift pulseincludes a first period between the first pulse and the second pulse. 5.The magnetic memory of claim 4, wherein the shift pulse has, during thefirst period, a third current value which is less than a threshold formoving the domain wall.
 6. The magnetic memory of claim 1, wherein thefirst pulse has the first current value during a first period from afirst time instant to a second time instant, and the second pulse hasthe second current value during a second period from the second timeinstant to a third time instant.
 7. The magnetic memory of claim 1,wherein a first pulse width of the first pulse is equal to a secondpulse width of the second pulse.
 8. The magnetic memory of claim 1,wherein the magnetic member is provided above a substrate, the firstdirection is a direction along a surface of the substrate, and thesecond direction is a direction crossing the surface of the substrate.9. The magnetic memory of claim 1, wherein the magnetic member isprovided above a substrate, and each of the first direction and thesecond direction is a direction along a surface of the substrate. 10.The magnetic memory of claim 1, wherein the magnetic member has acylindrical structure.
 11. The magnetic memory of claim 1, wherein themagnetic member has a plate-shaped structure.
 12. The magnetic memory ofclaim 1, wherein the magnetic member has a constriction structure. 13.The magnetic memory of claim 1, wherein a first volume of the firstportion is greater than a second volume of the third portion.
 14. Themagnetic memory of claim 1, wherein the first current value has amagnitude for the domain wall to move into the fourth portion via thefirst portion, and the second current value is less than the firstcurrent value and has a magnitude for the domain wall to move from thefourth portion into the second portion via the third portion.
 15. Themagnetic memory of claim 1, wherein the first current value and thesecond current value have a relationship:ia>A _(L) Jc>ib>A _(S) Jc where ia is the first current value, ib is thesecond current value, Jc is a current density of a threshold current formoving the domain wall, A_(L) is a maximum value of a cross-sectionalarea of the first portion, and A_(S) is a maximum value of across-sectional area of the third portion.
 16. A magnetic memorycomprising: a magnetic member including a first portion with a firstdimension in a first direction, a second portion spaced from the firstportion in a second direction crossing the first direction and having asecond dimension in the first direction, a third portion providedbetween the first portion and the second portion and having a thirddimension in the first direction, and a fourth portion provided betweenthe first portion and the third portion and having a fourth dimension inthe first direction; and a circuit configured to supply a shift pulseincluding a first pulse and a second pulse to the magnetic member, andto move a domain wall in the magnetic member in the second direction,wherein a first current value of the first pulse and a second currentvalue of the second pulse have a relationship:ia>A _(L) Jc>ib>A _(S) Jc where ia is the first current value, ib is thesecond current value, Jc is a current density of a threshold current formoving the domain wall, A_(L) is a maximum value of a cross-sectionalarea of the first portion, and A_(S) is a maximum value of across-sectional area of the third portion.
 17. The magnetic memory ofclaim 16, wherein the third dimension is less than the first dimension,and each of the second dimension and the fourth dimension is less thanthe third dimension.
 18. The magnetic memory of claim 16, wherein thesecond pulse is supplied to the magnetic member after the first pulse issupplied to the magnetic member.
 19. The magnetic memory of claim 16,wherein a first volume of the first portion is greater than a secondvolume of the third portion.